Crystal chemistry of magnetic oxides part 2: Hexagonal ferrites

Crystal chemistry of magnetic oxides part 2: Hexagonal ferrites

Prog. Crystal Growth and Charoct. 19e5,Vol. 11, pp. 155-205 0146-3535/85 $0,00+ .50 Copyright © 1986Pergamon Journals Ltd Primed in Great Britain, ...

2MB Sizes 6 Downloads 33 Views

Prog. Crystal Growth and Charoct. 19e5,Vol. 11, pp. 155-205

0146-3535/85 $0,00+ .50

Copyright © 1986Pergamon Journals Ltd

Primed in Great Britain, All rights reserved

CRYSTAL CHEMISTRY OF MAGNETIC OXIDES PART 2: HEXAGONAL FERRITES E. P o l l e r t Institute of Physics, Czechoslovak Academy of Sciences, 180 40 Prague 8-LibelS, Na Slovance 2, Czechoslovakia

(Received 11th April 1986)

This

article

tled

"Crystal

is a c o n t i n u a t i o n Chemistry

General

Problems

Crystal

Growth

of

the f i r s t

of M a g n e t i c

- Spinels"~

Oxides~

published

and Charaoterizatio~

part

enti-

Part

i:

in P r o g r e s s

Vol.

9~ PP.

in

263-

323 (1984). ABSTRACT

Hexagonal

among ture

are

the m a g n e t i c

types

by cations

of layers~ the r a t i o

distinguished. i n g of

The

of c a t i o n s

chemical

are

cussed

basis

layer

part

have

structures in

units w deviations of some

part.

155

from

it l e a d s

part

of

sublattice positions

arising of

stack-

to

the

to the i n f l u e n c e

on the r e s u l t i n g

stacking

"mixed"

to be

and polytypes.

the f i r s t

is d e v o t e d

Defects

two

a large

particularly

the o x y g e n

in the last

sub-

Thus

and following

coordinated

and structures

struc-

size.

to c a t i o n s

into

properties.

of t h e i r

a n i o n i c 2 the o t h e r

6-fold

the l a y e r s

group

partially

S~ R a n d T g i v e s

discussed

second

of the r e g u l a r

structural

important

anions

arrangement

blocks

entering

between

ruption

merry

one p u r e l y

of m i x e d

CUl~Jing 4~ 5 a n d holes

Common

of o x y g e n

of the s t r u c t u r e }

problems

article.

and

of the s u i t a b l e

Their

the f o r m a t i o n These

large

3:1 of a n i o n s

the a r i s i n g

versatility

a

oxides.

is the s u b l a t t i c e

stituted

with

ferrites

due

crystalloto the

the b l o c k s the i d e a l

related

o r ooin the

phases

inter-

or

stoichioare

dis-

156

E. Pollert

CONTENT

i.

Introduction

2.

Basic

feature

2.1.

The

S, R,

2.2.

Stacking

of

the

of

the

blocks

2.2.1.

Identical

blocks

2.2.2.

Different

blocks

2.2.3.

Mixed

3.

Hexagonal

4.

Cations

layer

structures

ferrite

region

in h e x a g o n a l

4.1.

Heavy

cations

4.2.

Small

cations

5.

structure

and T blocks

Defects

ferrite

and related

5.1.

Stacking

5.2.

Nonstoiohiometry

5.3.

Related

structures

faults

structures

i.

Hexagonal The

ferrites

reason

for

mixed

layer

great

number

that

such

solid gated nally the

are

of v a r i o u s

until

now.

years

from

Beside

particular

like

or perovskites.

common

composed

basis

of

two

anions)

the

"heavy"

cations

anions)~ pical

second

between

size.

the

BASIC

to an

layers

are

sublattices.

enormous

related

includes

of

One

number

the

we

now

also

OF

THE

size of

see

part

was

covering

structures

the

compounds.

structural

ferrites

one

being

the

oxygen

comparable these

small

origi-

during

type

two

is a f r a m e w o r k

formed

merely

anions with types

that of

by

interstitial

oxygen

substituted of

layers

cations

by

oxygen

conveniently d e n o t e as a " b l o c k " .

placed

and

investi-

STRUCTURE

the h e x a g o n a l

of

a

easily

can

nonmagnetic

rather

to p l a c e

of c o m p o u n d s

hexagonal

denotes

first

sequence

which

a possibility

ferrites,

fourth

formation

of

and

of h e x a g o n a l

the

has

of

oxides.

existence

group

the

cations

the m i x e d

small

layers~ one

among

properties~

a relatively

FEATURE

i. A d e f i n e d

the

several

ferrites

structure

of

layer

(i.e.

Fig.

structural

cavities able

see

of

types

group

only

of

and

hexagonal

2.

The

rise

the

spread

the n a m e

spinals

into

oxides

Consequently

large

of p o l y t y p e s

which

this

iron

widely

extremely

cations gives

series

INTRODUCTION

erystallochemieal

formation

a versatility

only

an

their

struotures~

solutions

last

represent

this

structure

is a tyIn

the

of a s u i t -

Crystal chemistry of magnetic oxides

157

@[email protected] Fig.

i. A r r a n g e m e n t

of M + ions in a c l o s e p a c k e d M - 0

layer O-oxygen 2.1. T h e

@ -

heavy cations

Sf R a n d T b l o c k s

The S-block~

in fact a (iii)

Fd~m) 2 c o m p r i s e s cupied

anions,

tetrahedral

from possible

slice of the cubic s p i n e l s t r u c t u r e

(space g r o u p

two close p a c k e d l a y e r s of o x y g e n a n i o n s w i t h p a r t i a l l y ocand ootahedral

sites b e t w e e n

the layersg

2 tetrahedral

16 a n d 4 o o t a h e d r a l

from possible

8 (see Fig.

2).

0

0

I

9

$

( Fig. The R-block middle Coulomb

2. S-block,

consists

one c o n t a i n i n g energy

@-

8a,

of three layers~ a h e a v y cation.

the c u b i c s e q u e n c e

c a t i o n s h a v e to b e r e d i s t r i b u t e d .

O-

16 d

the o u t e r two p u r e l y a n i o n i c

and the

Due to an effort

the

to m i n i m i z e

of l a y e r s is no m o r e p o s s i b l e Consequently

one f r o m the f o u r

and the s m a l l [ii~

di-

158

E Polle~

rections

originally

and

the f o l l o w i n g

then

Fig.

equivalent types

is p r e f e r r e d ,

the

of o c c u p i e d c a t i o n i c

structure sites

becomes

are

hexagonal

created,

see

3:

::i Fig.

-

Octahedral distances

3- R - b l o o k ,

sites are

tribution that

shared

cations

sites

tetrahedra. In fact

sites

displaced

,~0.16

us n o t e

that

higher

the o c c u p a n c y

coordination

the c a t i o n s

trahedral

is l a r g e r

sites.

of

than

faces.

Their

sites

have

energy

con-

to b e h i g h e r

than

sites. formed by

distributed position.

cations

of t w o a d j a c e n t tetrahedral

the o c t a h e d r a l

Hence

octahedral sites.

The

environment.

the f a c e

either

between

and has not

it w o u l d be b e t w e e n

mutual

octahedra

the C o u l o m b

in s u c h p o l y h e d r a

the c e n t r a l

to t h e s e

adjacent

number

placed

statistically

~ from

be ascribed

of b o t h

Consequently

octahedral

2b (2d)

the o c c u p i e d

in t r i g o n a l b i p ~ T a m i d s

cations

or t h e y a r e

to the o c c u p a n c y

block.

in t h e R - o e t a h e d r a l

the c - a x i s

Let

those among

in the s p i n e l ' s

coordinated

5 cannot

shared by common

than

the s p i n e l

along

number

of

in

lower

of the c a t i o n s

of the

- Five-fold

in the o e t a h e d r a

obviously

shared by edges

12K, (6g), ~-4fvi, ~ -

@-

the

oscillate two

the c o o r d i n a t i o n

usual meaning.

sites reason Also

two o c c u p i e d

is p r e f e r r e d for

this

is

the d i s t a n c e adjacent

te-

Cw=alchemistw ~ magn~icoxides -

Ootahedral

sites

in

the

combination)

with

placed

slightly

there

nel block

The T-block of o x y g e n among

three

respective

because

octahedra

differ

of f o u r

from

oxygen

is r e p l a c e d

sites,

between the adjacent

one

lying

nearest

layers,

by a heavy

tetrahedral

shared

those

of the d i f f e r e n t

consists

anions

interface

b y edges.

(usually

Energies

in s i m i l a r

sites

in e a c h i n t e r i o r

cation.

Small

$-R

of c a t i o n s

of the spi-

layer

cations

and two O c t a h e d r a l

are

(see Fig.

one f o u r t h distributed

4). T h r e e

®

I

18~i,

blocks

neighbours.

® Fig. 4. T-block, ® -

159

~ - 6 c~, ~ - 60w,

~-3bvi

ions

placed

central

ootahedra. outer

in

cation Let

the o c t a h e d r a l placed

us n o t i c e

oetahedral

tribution

because there

hedral

and

lie

The former

of an e l e c t r o s t a t i c

exist

tetrahedral

on a v e r t i c a l

threefold

sharing

of

the ener6~y d i f f e r e n c e

positions.

Obviously

sites

in the o o t a h e d r o n

again

energy

positions

one has repulsion

differences

in T a n d

faces between

a higher with

axis

with

the

two a d j a c e n t

the c e n t r a l Coulomb

a~d

energy

neighbouring

between

S blocks

the

cations.

the o c c u p i e d

and occupied

the con-

octa-

octahedral

160

£.Poile~

sites

in the i n t e r f a c e

(see Fig. sharing

5).

As

between

the a d j a c e n t

in the p r e v i o u s

of the r e s p e c t i v e

case

this

blocks

(usually

originates

from

S-T combination), the d i f f e r e n c e s

in

polyhedra.

C A

0

T c S

A

!

C

B

A

B T A

B

Fig.

5. C h a n g e

of the s t a c k i n g

introduction

sequence

due to the

of h e a v y

cations

into

rotation

of R - b l o c k

the o~cygen

sublattioe, indicates

the h e x a g o n a l

Structures o-axis

of the b l o c k s

vertical)

interactions layers

are to

and influence

A total

survey

dual b l o c k s Examples charge

lead

compared

in

6. One c a n

the s t a c k i n g

the r e d i s t r i b u t i o n

of the o c c u p a n c y

to v a r i o u s

(cross-sections

in Fig.

the c h a n g e

S~ R a n d T a n d

of the b l o c k

due

S, R a n d T

b y 180 ° a b o u t

axis

[[lO]

easily

of the r e s p e c t i v e

with

the C o u l o m b

of the r e s p e c t i v e

cations.

sublattioes

between

them

in the i n d i v i -

is g i v e n

compositions

demonstrate

a variation

valencies

the p r e s e n t

ions.

of

direction

see w h y

sequence

of s m a l l

on the i n t e r f a c e

in

of

in T a b l e

their

I.

resulting

Crystal chemistry of magnetic oxides

161

6 Fig.

2.2.

The

Stackin~

of

individual

gative combine

S-phase,

blocks

to a t t a i n is less

and TS

units

0-

8a,

O-

16d

the b l o c k s

or t h e y can be

blocks

tion

6.

can bear

an u n c o m p e n s a t e d

electrically

neutral.

the e l e c t r o n e u t r a l i t y ~

strongly

seems

to be

of the C o u l o m b

forced.

energy

e.g.

Nevertheless

in a n y case is l o w e r

that

either

the c h a r g e d

$2+R2-~

positive blocks

ordering

a regular

slightly than

charge

While

favoured

stacking because

for stacked

or ne-

have

to

of the n e u t r a l of m i x e d R S the c o n t r i b u -

identical

blocks

R

and T respectively.

2.2.1.

Identical

electrically posed. nent

Actually

systems.

blocks.

neutral this

Apparently

if no l o c a l m a y n o t be

the s t a c k e d

variations true~

S, R and T b l o c k s

of t h e i r

particularly

compositions

in the case

have are

to be sup-

of m u l t i c o m p o -

162

E. P o l l e r t

o 0

o

o

,-t

+

0

-H

I

o

0 +

o

'I I C~O0 o -I~'~ ~'~ @

+

+ C~t .

i I ¢'~00 0 -I-

@ @

N

i

I

I

I

I

I

o 0 •H

k 0)

0

o o .H ~

o

O0

.H 0 o 0 ~ ,o

0

'~

o H

4.~ H

H

~

H

o o 0

o

~

o

"~

4~ -~

~o

.~"

~o

~o

-~"

-~

~o

~o

.~-

~o

~o

0 0 0

0 4.~ C~ .H 0

o o

4~

I

I

I

I

I

I

I

I

I

I

!

I

i

I

Crystal chemistry of magnetic oxides

0 o ,-I

163

I

0

0 oz~=l 0 4-~'~

o

I ~t

I

+ • ~

o 0

I ~,1

+

+

O

@

I-~" +

d)

+

+

+

,~

~ 0

I~

0

'

I

:~

I

I

i

0

I..~" 0

+ ~b-

+

¢

~

@ +

I !

v

+

o'~

= o

(9

~:

:~ I I :2E:I I

i

I.~" {'~I

4.~

+

~:11

4.) o =

~: I

o ,M •H



0

,-.I

II

0

,-I

o,t

o 0 0

0 ,,4

,o

,-I

,-I r.,.l o

®

• i1)

~

•1-1

o

o

@

I

O

H

@ ,-t

® o ,I-I I-I

I-t

~

H

H

e ot

~

~

c',t

',o

,,-I

~

',o

c~

H I:~ ,1:I

,,-I

o

~

4o

Q

0 ~

o

o

o o 0

v

o

O -H 4.~

o M

0 o

~.~

v

v

v

!

I

I

I

I

I

i

I

I

I

I

I

!

i

~

v o

~

4a

e

o

164

E. PolIeR

The

S-phase.

structure. with

is in fact

In this [iii]

the

in this

This

cubically

The R-phase.

feature

In this

mutually

• ~

case

rotated

spinel

the s e q u e n c e

(see Fig.

is the r e g u l a r

elementary

elementary of

7) a n d

three the

cations.

relatively

small

~nd

than

is g i v e n

the

elementary

the

Because

ions

coincides The period i.e.

of

parameters

of two p u r e l y of this

the

value

oxygen

see

among

increase. compound

e.g.

/x/)



!~



Fig. 7. R-p~se,

@ - 4fvl, M - 2d, ~ -

6g

R

in i m p o r t a n t

layers

dista/Ices

repulsions

2+~

b y two a d j a c e n t

c-axis,

7.

ie

78

blocks~

lattice

is f o r m e d

in the B a F e 4 T i 2 0 1 1

theoretical

in Fig.

cell

the h e x a g o n a l

the i n t e r o a t i o n i c

of the b a r i u m

30 % g r e a t e r

x

cell

cell.

ah = ~ aeubie

alternating

heavy

ive v a l e n c y

,

b y 180 ° a b o u t

containing

structure

by

cube

of the s p i n e l

subsequently:

e h = acubi e

blocks

packed

description

of the h e x a g o n a l

of the u s u a l

is m a t e r i a l i z e d

layers

are r e l a t e d

the c - a x i s

direction

direction

six oxygen

case

only a different

a n d one cations

Thus was

the

the

layer become

effect-

fou/Id a b o u t scheme

of the

C w ~ a l c h e m i ~ W of magn~icoxides The T-phase. blocks

oan

One

w i l l be e v e n

presence

of h e a v y

ly existence probable. respond

expect

that

stronger

cations

us n o t e

to a s i n g l e

Table

mentioned

resulting

(s) 3

(2) 3

(R) 2

(3) 2 = 6

two

to h e x a g o n a l

Different

those t i.e. integral

five

On the o t h e r the same for

hand

reason

excessive

/or Y units

seen

The

As can be s e e n

layers. Layers

The

Its

and

the e l e m e n t a r y

the s t a c k i n g

e-axis 14.6o6

P63/mmo

BaFe4Ti2011

13.608

P~ml

Ba2Fe8014

are

three

9.69

of R a n d T b l o c k s of the T - b l o c k s energy

phases

cubic

of M a n d M

units

the e l e m e n t a r y

rotated

with

to two c h e m i c a l

known

type

of

of

J. Phys.

Chem.

67,

957

Stacking

packed

built

formula

mirror

the h e x a g o n a l

magnetoplumbite

diseussed~

symmetry

respect

cell

space

mineral

to be i m p r o b a b l e

for i.e.

of M a n d /

determined

layers

m a y be

description.

corresponds

group

as

segments.

cations

are

of

two of

and behave

already

and cubically schematic

constitutes

is the b e s t

seems

and hexagonal

the f o l l o w i n g

the f i r s t

stable

contribution.

a pair

heavy

are

of the o v e r - a l l

the h e x a g o n a l l y

combinations

only

as M a n d Y r e s p e c t i v e l y .

alone~

the o a x i s

composition

possible

However~

in the f o l l o w i n g

of the C o u l o m b

of

D.W.Eckart,

Hexagonal

of

Zn2Fe408

to e a c h o t h e r b y up f r o m units

ferrites

(1963).

ten

MMeI2019.

planes.

named

the a p p r o x i m a t e

PbFeT.sMg3.5019 "

xXJ.A.Kohn,

oct-

Fd3m

s i x l a y e r TS c o u p l e s

in two b a s i c

8 and from

to the i s o s t r u c t u r a l

to be im-

cell would

of

Example

TS a n d aT.

denoted

of o v e r l a p p i n g

containing

M-phase

from

there

RS,

the c o u p l i n g

sequence

f r o m Fig.

180 ° a b o u t

units

increase

b y the s e q u e n c e

M-phase.

Generally

as in the c a s e

results

that

Consequent-

in / x X / s e e m s

composition

of b l o o k s ~

l a y e r RS

structural

of e a c h block.

axes

blocks.

types

layers

Structure

4

different

of the

cell

6

=

T

2.2.2.

the

because

blocks

of l a y e r s x in

elementary

Xreferred

between

T-block.

2. P h a s e s

Number

blocks

repulsion

of R - s t r u c t u r e

only briefly

for completeness

identical

Stacked

in the c a s e

in two s u b s e q u e n t

of the s t r u c t u r e

Let

the e l e c t r o s t a t i c

than

165

according

composition

166

E. Pollert

!

i

--

A

B

® R~

)

(

@

F±~. S. ~-ph~,~,

@-

4fly,

O-

2~,

(9- Z2K,

Crystal chemistry of magnetic oxides hexagonal

packing cubic

.

.

.

~

.

.

acking

.

oxygen layers

M

M-units

MM~ I denotes

167

hexagonal

e l e m e n t a r y cell

layers c o n t a i n i n g h e a v y c a t i o n s

~indieates

rotation

and

of the b l o c k b y 180 ° about

the

o axis T h e Y phase. f r o m Fig.

Sequence

of h e x a g o n a l l y

9 and f r o m the f o l l o w i n g

p a c k e d l a y e r s may b e seen

and cubicaly

schematic

description:

hexagonal packing packing

.

-

-

-

-

-

I I I I I

I

Y1

Y2

I

-

-

oxygen layers

-

I I l

Y31

Y4

Y-units

(Y)3

T h e Y p h a s e has

hexagonal

the r h o m b o h e d r a l

cell

s y m m e t r y w i t h the e l e m e n t a r y cell s p a n n i n g

o v e r s i x layers~

see Fig.

used. T h e p e r i o d

then s p a n s o v e r 1 8 l a y e r s t i.e.

position

elementary

i0. H o w e v e r u s u a l l y

of the e l e m e n t a r y c e l l C o x T e s p o n d s

the h e x a g o n a l

description

tb_vee Y - ~ n i t s

is

a n d the com-

to three f o r m u l a units

M2~ez~°22. 2.2.3.

Mixed layer structures.

k i n d of b l o c k s

So f a r only the p h a s e s

or units w e r e d i s c u s s e d .

the s t a c k i n g of d i f f e r e n t

elements.

termed mixed layer structures.

c o n s i s t i n g f r o m one

We s h a l l n o w turn our a t t e n t i o n

to

Consequently the r e s u l t i n g p h a s e s are

168

E. Pollert

$z

T2

Fig. 9. Y-phase, @ - 6OlV, O - 3 a V I , , . @- 1 8 ~ i , ~ _ 6ov~ , 9 - 3bVi , @ - 6 o ~

Crystal chemistry of magnetic oxides

BJ

f

B'

LA o~

Fig. 9. (cont.

~

®

®

169

170

E. Pollert

$ T

S

-q

T

S T

Fig.

i0.

Relation

between

the rhombohedral

and

hexagonal

to t h e

existence

elementary c e l l s o f t h e Y - p h a s e Even ous

though

there

combinations

Therefore

Both

we

these

to M o r Y

can be

layers.

Basic

cases

(c-axis). of

the

derived

chains.

the

to b e n o

by

units

periodic

obstacles

of finely

composition

insertion

and

increase

more

of

of

the

ordering

ever

of varisince.

series.

structural

the structure

S have

and

units

in-

is p r o v o k e d

different

complicated

numbers

this

leads

of in

elementary c e l l d i m e n s i o n

compositions

various

up to

extraneous

the block

become

graded

but

of

a rearrangement

M, T

sequences

to a c o n s i d e r a b l e

same

the

Consequently

individual

Phases

evident

H S and M Y series were reported n p r r e s t r i c t o u r d i s c u s s i o n to t h e s e t w o

shall

because

some

seems only

as w e l l of

as polytypes,

the stacking

phases

elements

are

formed.

Due

to

over

this normal

a large

completed

by

stacking.

A special

applied

The

M

block it

diffraction

number

of

a method

S series.

The

in

is n e c e s s a r y

this

members

n M-units.

techniques

cells

determining

electron

successfully

with

unit

As

the

were local

microscope

giving

found

structural

to be

structure~ method,

data

insufficient internal

known

as

averaged and

had

regularity

lattice

to b e of

imaging

the was

case.

of

the

series

structure

to d i s t i n g u i s h

of

are

formed

the members

two cases i n odd

and n

by

combinations

depends even:

on

of

one S

the number

n

Crystal chemi~w of magnetic oxides

171

- n odd Insertion

of an S b l o c k

into

the M s t r u n t u r e

results

in a s e q u e n c e

s u c h as

. . . ABaABCA.CIACBABnABCABC B~ BAC~CABf B~ BA~CB • • •

I

F

I

M

The

complete

the

translation

axis. tion

--

The

I

M ~

repeat

M

period

in[il~

resulting

-r-i -f I tl tl

7--

I

S

M ~"

consists

direction

symmetry

corresponding

M

M

S "K"

of a p a i r

%.f'f

T

by

is h e x a g o n a l

to the f o r m u l a

. tI

tI

of b a s i c and

with

sequences

rotation

related

by 180 ° about

the e l e m e n t a r y

cell

by C

eompesl-

(M S)2~,

n even The

sequence

of l a y e r s

is

•.. C B A ~ A B C A ~ A C B A C B C ~ C A B ~ A C ~ A C ~ C A B C B ~ B ~ C B . . .

II I

I

I

s 3 ~1 with M structures in

[~i0]

n even. is used.

Then

Phases

listed

ing

to the m o s t

Let

us

phases

MMMMS,

that

repeat

3 and

important

period

etc.

consists

by

the t r a n s l a t i o n

of l a y e r s

is h e l d

the h e x a g o n a l of three

M4S

end member

for any

description

basic

sequences

magnetoplumbite

s t r u c t u r e t i.e.

ferrites

M and

sequences

of the p h a s e

related

usually

including

of

s3

as

description.

in h e x a g o n a l

various

M3

repetition but

the W - t y p e

a permutation

II I.~I.

the S b l o c k s

. Similar

in the s e r i e s

because

MMMSM~

of

I

I s2 M3

is r h o m b o h e d r a l

in the T a b l e

note

~2

side

~

II

I.I

in the s c h e m a t i c

identified

are

new

by

the c o m p l e t e

above

I

M * s1 M 2

~-~

structure

it is s h o w n

I

on e i t h e r

direction The

II

I

S units

of the same degenerate

(MS)2

M-phase

phase

belong-

is s h o w n

in Fig.

ii.

does

lead

formation

not

total

upon

to

composition,

repetition

into

of

e.g. the same

structure.

T h e M p -Y r s e r i e s . reasons -

the r a t i o

-

phases tors ve

This

M

: Y varies

in the s y s t e m

determining

units.

extended

Nevertheless

let

in a r e l a t i v e l y

exhibit

their

In a n o t h e r

to the f o r m a t i o n

dency

is an e n o r m o u s l y

system

for

the f o l l o w i n g

:

structure:

words

f o r no a d j a c e n t

of

that

there

and ordering

their

stacking

are

two f a c -

of the r e s p e c t i sequences

leads

phases.

that v a r i a t i o n

M-units

range

it m e a n s

composition

a permutation

of p o l y t y p i o

us n o t e

large

polytypism,

of

the s t a c k i n g

to b e p r e s e n t .

The

reason

is l i m i t e d

b y a ten-

is e n e r g e t i o a l .

For-

E. Pollert

172

i

fR

'S*

B'

tRq

Fi~. 11. W-pm~,~, O - 4fry, ~ - 4d, O - 4~, Q - 6~, (D- 12~, ® - 4fvl, }~- 2d, t~ ~ indioate translation in [~lO]direotion by a h . ~6

and rotation by 180 ° about c axis.

Crystal chemistry of magnetic oxides

173

tR*

S

S

--B'

R

F

L--A

_J

F±~. 11.

(cont.)

E. Pollert

174

marion

of M c h a i n s

lowering

of

the

would

entropy

lead termj

to a n the

increase

(U + PV)

of

the

Gibbs

contribution

energy

remains

because

of a

obviously

un-

changed.

Table

Stacked

M

3.

blocks

: S

Structures

Number

of

layers

in

stacking

elementary

sequence

cell x

i : i

(~s)2

(7) 2

2 : i

(~2s)3

3

:

i

(~3s)2

4

:

1

5

:

1

6

: 1

1

: 0

Structure

Example

Hexagonal

of

composition

= 14

c axis

[~]

HI

BaZn2Fe16027

32.85

R1

Ba2Zn2Fe28046

84.11

(17) 2 = 34

HI

Ba3Zn2Fe40065

79.40

(N4S)3

(22) 3 = 66

R1

Ba4Zn2Fe52084

153.90

(Mss)2

(27) 2 = 5 4

HI

BasZn2Fe640103

125.80

(M6S)3

(32) 3 = 96

R1

Ba6Zn2Fe760122

223.40

(~)2

HI

BaFel2019

M2

Xreferred

in M S s e r i e s n

to h e x a g o n a l

io

=

23.20

axes

H 1 - P63/mmc , R I - R~m Similarly

as f o r

influence

on

combinations sequences

S series various oomblnations of the M a n d Y u n i t s h a v e an n resulting structural properties. Generally two t y p e s ~ i.e.

of o d d

have

Odd number neral

M

the

to b e

and

even numbers

of M - u n i t s

with

Y u/lits~

in the b a s i c

distinguished.

of M b l o c k s .

Basic

sequence

can be

expressed

according

to

the

ge-

and

the

fol-

formula

(MM~)aMY3c+d where

The

a = O~

complete

lowing

cases

i~

2

... n;

repeat have

e = 0,

period

to b e

i~

2

consists

... n a n d

of a p a i r

d = 0~

of b a s i c

considered:

d = 0

' ,, M

M~

M

YI

,

1 ,'Jo

Y2

Y3

i 8/Id 2

sequences

175

Crystal chemistry of magnetic oxides ~tBeA'~AOI~C~BAIC'~C~AC~I1

I

I ~°

symmetry operation:

I

I

-~

I

I =c

r o t a t i o n b y 180 ° a b o u t c h axis,

d =i

M

M ~"

M

YI

Y2

Y3

tj tI ~" t_[~ ~ I ~I symmetry

operation:

d = 2, w i t h o u t

translation by

I

I

I

M

YI

Y2

s y m m e t r y operation:

I ~J°J

~

loss of g e n e r a l i z a t i o n

a n d r o t a t i o n b y 180 e a b o u t c axis,

we may choose a = 0

It Jt *M

rotation

YI

•YI

it ~Y2

b y 180 ° a b o u t e axis and t r a n s l a t i o n b y a--~33 in

E~lO] direction. Even number

of M b l o c k s .

Basic sequence

c a n b e e x p r e s s e d b y the g e n e r a l for-

mula

S i m i l a r l y as in the p r e v i o u s quence corresponds

cases it can be s h o w n that

to the c o m p l e t e r e p e a t

t r i p l e d if d is 1 a n d 2. T h e n lations

of ~

Consequently

and

a ~ 3

the b a s i c

sequences

Table

the c l a s s i f i c a t i o n

are r e l a t e d b y the trans-

of i n d i v i d u a l

phases

according

f o r the s i m p l e s t

to the s p a c e

c a s e of M 2 Y r

in the f o l l o w i n g T a b l e 4.

4 illustrates

elements

se-

it must be

respectively in the [~10] direction

g r o u p s c a n b e d e d u c e d as it is d e m o n s t r a t e d subgroups

the s i m p l e b a s i c

period for d = 0 while

c l e a r l y the r e l a t i o n b e t w e e n

and f o r m a t i o n

of p o l y t y p e s

c a n b e done f o r o t h e r s u b g r o u p s .

the o r d e r i n g of the s t a c k i n g

in the M 2 Y r series.

However

A similar analysis

the p r o b l e m b e c o m e s m o r e c o m p l e x

176

E. Pollert

because

if n u m b e r s

arrangements structures

for

for M8Y27.

If p > 2

are possible. even and

of M a n d Y u n i t s

increases

too. T h u s

the c o m p o s i t i o n From

the u n i t s

increase

there

M2Y4,

three

additional

these

the

third

distributed

the n u m b e r

are possible

eleven space

for M2Y21

groups,

one r e q u i r e s

so as to s u p p o r t

of p o s s i b l e

three

different

and more

namely

special

R3m,

than

plane

4. C l a s s i f i c a t i o n the s p a c e

Coefficients

e I ~ 02,

O 1 = e2,

~2Yr ° 1 ,2

=

Space

d I ~ d2

=

= MY3oI+dl

group

R~m

R~m

d I ~ d2

02 , d I

P~m

P63/mmc

d2

according

Examples

M

the v a l u e s

mentioned

: Y

MMY 4

2:4

MY2MY 3

2:5

MY2MY 4

2:6

MMY

2 : 1

MYMY 2

2:3

MY2MY 4

2:6

MMY 3

2 : 3

MYMY 4

2:5

MMY 6

2

MYMY

2 : 2

MY2MY 2

2

MY3MY 3

2:6

MY302+d 2

dl~ 2 c a n r e a c h

to

groups

c I ~ 02 , d I = d 2

eI

of M 2 Y r x p h a s e s

above

f o r e~

d.

n must

to ~ a x i s ~

MYMYMY2MY2MYMY

Table

400 000

P3ml and P~m2

conditions:

a mirror

stacking crystal

: 6

: 4

be e.g

177

Crystal chemistry of magnetic oxides Table

Stacked M

: Y

blocks

5- Phases

in M Y series p r

Number

of

layers

in

stacking

elementary

s e queno e

ceil

Structure

Example

of

Hexagonal

composition

2 : I

MMY

(16) 3

RI

Ba4Zn2Fe36060

113.16

2

MMY2

(22) 3

RI

Ba6Z~4Fe48082

156.75

MYMY

(11) 2

HI

:

2

2 : 3

2 : 4

2 : 5

MMY 3

200.4

MMY 4

(34) 3

RI

MYMY 3

(34) 3

RI

244.0

MY2MY 2

(17) 2

HI

81.3

MMY 5

(40) 3

RI

MMY 6

4o

(40) 3 46

BalOZn8Fe720126

Ba12ZnlOFe840148

244.0

287.7

H2

95.9

R1

287.7

H

Ba14Zn12Fe960170

ii0.6

MYMY 5

(46) 3

R1

331.8

MY2MY 4

(46) 3

R1

331.8

MY3MY 3

(23) 2

H1

110.6

MMY 7

(52) 3

R1

MYMY 6

(52) 3

R1

375.0

H2

125.0 375.0

52

MY3MY 4

(52) 4

R1

MMY 8

(58) 3

R1

MYMY 7

2:9

66.8

RI

MY2MY 5

2 : 8

Ba8Zn6Fe600104

(28) 3

MY2MY 3

2 : 7

H2

MYMY 2

MYMY 4

2 : 6

28

52.25

58

Bal6Znl4Fel080192

Bal8Znl6Fel200214

375.0

418.5

H2

139.5

MY2MY 6

(58) 3

R1

418.5

MY3MY 5

(ss) 3

R1

418.5

MY4MY 4

(29) 2

HI

139.5

MMY9

MYMY 8

64

H2

192

R1

Ba20Zn18Fe1320236

154.1 462.3

178

E. Polle~

Table 5 Staeked blocks

N u m b e r of

(eont.) Structure

layers in M : Y

2 : i0

s t a c k i n g sequence

Hexagonal

composition

o

axis

elementary oell

MY2MY 7

192

R1

462 -3

MY3MY6

64

H2

154.1

MY4MY 5

192

R1

462.3

MMYI0

(7o) 3

R1

MYMY 9

(7o) 3

R1

535 •8

H2

178.6

MY2MY 8

2 : 21

Example of

7o

Ba22Zn20Fe1440258

535.8

MY3MY 7

(70) 3

R1

535.8

MY4MY 6

(7o) 3

R1

535.8

MY5MY 5 MYMY20

(35) 2 (136) 3

HI

178.6

R1

Ba44Zn42Fe2760500

982.5

MY3MYI 8

136

H2

4:3

M M ~

(38) 3

R1

BalOZn6Fe840142

269 -9

4 : 5

MYMYMYMY 2

(50) 3

R1

Ba14ZnloFe1080186

357.0

4 : 6

~ 2 M Y 2

56

H3

Bal6Znl2Fel200208

133.4

4 : 8

MYMYMY3MY 3

68

H3

Ba20Zn16Fe1440252

162.6

327.5

MYMYMY2MY 4

(68) 3

R2

487.8

M Y M Y 2 MY 2 MY4

(68) 4

R2

487.8

4 : 9

MYMYMYMY 6

R1

Ba22Zn18Fe15602741

531.4

4 : lO

MMYMY2MY 7

(74) 3 80

H4

Ba24Zn20Fe1680296 !

191.6

MYMY2MY2MY 5

(80) 3

MYMYsMY2MY 5

(98) 3

R1

MY2MY4MY2MY 5

(98) 3

R1

4 : 13

574.9 Ba30Zn26Fe2040362!

705.7 705.7

4 : 15

MYMY2MY3MY 9

(11o) 3

R2

iBa34Zn30Fe2280406

4 : 33

MY6MYIoMY7MYIo

(218) 3

R1

Ba70Zn66Fe4440802

6 : 8

MYMYMYMYMY2MY 2

78

H3

Ba22Zn16Fe1680290

185.6

6 : 13

MYMYMY2MY3MY 5

(lOS) 3

R2

Ba32Zn26Fe2280400

775.2

6 : 14

MYMYMY2MY3MY2MY 5

(114) 3

R2

Ba34Zn28Fe2400422

818.8

8 : 27

M3Y4MYT(MY)2MY6MY 8

(202) 3

R2

Ba62Zn54Fe4200740

H 1 - P6 /mme, H 2 - P~ml, RI - R3m, R 2 - R 3 m

H 3 - P~m2, H 4 - P3ml

792.9 1577

1455

179

Crystal chemistry of magnetic oxides

3- H E X A G O N A L

The

extent

of the h e x a g o n a l

existin G phases

csn be seen

MMe204-Me304-Me02 te p o s i t i o n s (phases) series.

Given

The

from

points

A~

and principal

S~ R, T,

6. T h e

fundamental

a m o n G the

of the s y s t e m letters

structural

indicaunits

Z b e l o n g i n G to the M S a n d M Y n p r W a n d B~ U r e s p e c t i v e l y d e n o t e the e x t r e m e c o m p o s i t i o n s

reported

X,

relations

diagram

12 t see also T a b l e

blocks

of BraLun p h a s e s

the s e r i e s

region

REGION

the c o m p o s i t i o n a l

the FiE.

of the i n d i v i d u a l

M~ Y a n d

in e a c h of

in

ferrite

FERRITE

W, U~

up to now.

Me02

7

o 20

Fig.

12.

40

Compositional

tool %

diagram

MMe204-Me304-Me02, phases

Obviously

the

of b l o c k s

combinations

defect ed b y

diagram

structures the

example

see T a b l e

reflects

80

of the s y s t e m

notation

the i n d i c a t e d

of

6.

only part

o r units

have

60

as w e l l

of as

to be c o n s i d e r e d .

the p o s s i b i l i t i e s tendency

The

of two n o n s t o i c h i o m e t r i o

latter

M phases

and further

to the f o r m a t i o n possibility included

of

the

is i l l u s t r a t -

into

the

diagram

/i/. Their

ideal

culated

the a c t u a l single

compositions

from

the

one following

crystals

corresponding

determined

are

content

from

denoted

to the R / S

and T/S

of Pb 2+ c a t i o n s

the c o m p l e t e

by points

K'~

chemical L'.

denote

blocks points

analysis

ratios

cal-

K, L w h i l e

of the p r e p a r e d

E. Polle~

180

Table

6. Phases m a r k e d in the c o m p o s i t i o n a l

diagram

MMe204-Ne~O4-Me02

Phase

Examples

of c o m p o s i t i o n

Structural

S

Me2+Me3+04

s3

R

M2+--e3+-M 4 Me24+ 0 ii

RR "N"

T

T

M

M 2 + _ 3+2 M e 8 u14 3+ MMel2019

X

M 2 + _ 2 + _ 3+2 Me2 M e 2 8 u 4 6

MM'~"

Y

h2+. 2+. 3+^ Me 2 M e 1 6 u 2 7 M 2 + _ 2 + _ 3+n 4 Me2 M e 3 6 v 6 0 M 2 + _ 2 + _ 3+~ 3 me2 m e 2 4 v 4 1 M3+-- 2+--3+~ 2 Me2 M 1 2 u 2 2

M(K)

Pbl.14(Fe,Ga)ll.93018.86

M(K')

Pbl.14(Fe3+,Ga3+)ll.83018.86

~(L)

Pb0.85(Fe,Ga)12.45019.15

W

U Z

M(L')

(Ms) 2

(TS) 3

Ml 5 8Y35

M170S72

Pb0.85(Fe3+Ga3+)12.21019.15

4. C A T I O N S In p r i n c i p l e rites

unit s e q u e n c e

have

two types

IN HEXAGONAL FERRITE STRUCTURE

of c a t i o n s

to be d i s t i n g u i s h e d :

and s m a l l c a t i o n s

in the c r y s t a l

heavy cations

occupying holes

lattice

entering

in the f u n d a m e n t a l

of h e x a g o n a l

the o x y g e n

fer-

sublattice

m a t r i x of o x y g e n

anions.

4.1. H e a v y c a t i o n s Substitution

of h e a v y c a t i o n s

introduction

of d e f e c t s

the G i b b s

into

f o r o x y g e n a n i o n s can be in fact r e g a r d e d the oA-ygen s u b l a t t i c e

energy particularly

contribution.

Consequently

due to the s t e r i c

in o r d e r to p r e s e r v e

this effect has to be m i n i m i z e d b y a m u t u a l charge

of cations.

decrease trostatic

An i n c r e a s e

of the v a l e n c y attractive

nation polyhedra.

term PV a n d C o u l o m b the c l o s e p a c k e d

of

energy

structure size and

of the ionic r a d i i m u s t be c o m p e n s a t e d b y a

of c a t i o n s

The relation between

entering oxygen sublattice

as an

to an i n c r e a s e

i n t e r p l a y of s u i t a b l e

and v i c e v e r s a b e c a u s e

forces

leading

is o b v i o u s

of an i n f l u e n c e

on the m a g n i t u d e

the b o t h p r o p e r t i e s f r o m the Fig.

13.

of the elec-

of r e l e v a n t

coordi-

of h e a v y c a t i o n s

Crystal chemistry of magnetic oxides

o

oo

v

ELI

o

o

o

IM ~

o

m o B.

Pb

o K

No L

0

I

I

most

13.

frequent

guration

only

the

of

case

ferrites

given

Pb 2+ c a t i o n s

of

and

regard

to

troduction too

small

of so

St2+

in

the Table

lattice

deduced

than

Thus by

7.

from

to

cations

the

pure

into

CaMel2019

to

their

anions

ionic

hand

electron

can be

contribution

radii Be-

can

and

e different

c values

to an

to e x p e c t

of

confi-

considered

be

St-

in due

seen

from

hexagonal

behaviour

of

PbFel2019.

optimum from

Pb-O

distance,

e simple

combination

ions.

the

the

the

radli lit]

and valency

respective

leads

C a 2+ i o n s

into

simultaneous

of

a and

Pb 2+

radii

i

l

1JJ k)n¢

regard

of

possible

of

I

i

Pb 2+ a c o v a l e n c y

other

the b o n d

effects

introduced

the the

be

I

oxygen

influence

On

magnitude,

divalent

With

for

@ CI

17

ionic

parameters

it w o u l d

charge

the

while

A pure

the

I

i

surrounding

(p6)

o o Te Ro

1.6

cations.

with

earth

their

only

represent

oxygen

lattice does

presence

of

sublettice. the

not

e lower

close

exist

other

limit They

packed

and

the

suitable

for

are

the

already

structure

structure

cations

in-

like

is

can

be

B e 2+,

L a 3+ .

Originally was

divalent

exists.

that

destabilized. preserved

cations

of o o v a l e n c y

longer

t/~e s i z e

With

between

of h e a v y

of

can be

A contribution probably

Relation

bond

i

I

15

alkaline

comparison

I

'IA

are

ionic

to 6s 2 e l e c t r o n s the

I

13

Fig.

The

,

I

t2

181

the

reported

containing

existence

/2-4/

H-phase

but

of

ideal

recently

requires

solid

it w a s

in f e e t

• 0 . 6 U2_a O2.+4+F e l3 l+ . 6 U^128-. 4

solutions shown

formation

(H =

of

that of

the

formula

e stability defect

Ba 2+, Sr 2+)

Ml_xCaxFel2019

of

the

calcium

structures

llke

sublattice

forming

/5/

and L

3+

_ 2+

Supposing

that

the

skeleton

frame

~ 2+

- 3+

ao.341UaO.814reo.228rell.617 the

existence of

the

O 19

of vacaalcies

structure

is

on

/6/ the

exeluded~

oxygen these

chemical

formulas

give

182

E. PolIeR

Table

7. I n f l u e n c e cations

of the ionic radii

on the lattice

hexagonal Composition

of divalent

parameters

heavy

of some

ferrites

Lattice

parameters

Ref.

a

c

BaFel2019

5 • 890

23.20

1

PbFel2019

5 • 891

23.12

1

SrFel2019

5 • 864

23.031

2

BaCo2Fe16027

5.88

32.84

3

SrCo 2 Fe16027

5.88

32.76

3

Ba3Co2Fe24041

5.88

52.31

3

Sr3Co2Fe24041

5.88

52.05

3

rxii(Ba

2+

) = 1.61 A, rxii(pb2+)

i. E. Pollert,

unpublished

2. F. Bertaut, Radium 3. M.A. SSSR, 4. R.D. +

20,

R. Pauthenet,

A.I.

Agranovskaja,

Neorg.

Mat.

2, 1612

Acta Cryst.

and the all f o l l o w i n g

no evidence

about

/4/+

S. Pickart:

J. Phys.

(1959)

Virmik,

Shannon,

= 1.44 A,

results

A. Deschamps~ 404

= 1.49 A, r x i i ( S r 2+)

A.P.

Erastova,

Izv.

Akad.

Nauk

(1966) A 32,

751

data of ionic

the real c o m p o s i t i o n

(1976) radii

and have

in the article.

to be retrritten

into

the f o r m

0.619UaO.412~ell.959u18.969 and 3+ 2+ 2+ 3+ Lao.339Cao.809Feo.226Fell.54018.852 or d e s c r i b e d as m i x e d layer s t r u c t u r e s M I 2 3 Y 5 and M21Y5 respectively, c o n t a i n i n g about 0.2 % of iron vacancies. C o n s e q u e n t l y one can deduce the s t a b i l i t y where

local

of

"calcium h e x a f e r r i t e "

deformations

h e a v y cation.

are s e t t l e d

is e n h a n c e d

by p a i r i n g

b y the p r e s e n c e

each that

of T-blooMs

of Ca 2+ w i t h a n o t h e r

suitable

Cw~alchemist~ of magneticoxides Importance

of the r e l a t i o n b e t w e e n

respectively

is o b v i o u s

lattice by trivalent

replaced

with a decrease

the c o m p o s i t i o n

per limit of

of the o x y g e n

sub-

14 t h e i r s o l u b i l i t y

in B a F e l 2 O l q

decreases

sig-

in the size of ions so that B a ~+ can be c o m p l e t e l y

o n l y b y L a 3+ ions /7-9/.

rite where

of h e a v y and s m a l l c a t i o n s

of the o c c u p a t i o n

r a r e e a r t h ions.

As one can see f r o m the Fig. nificantly

the m a g n i t u d e

f r o m the c o u r s e

183

A s i m i l a r r e s u l t was o b t a i n e d f o r lead fer-

P b S m 0 ^~Fe311+ 8Fe20+06018 92 c o r r e s p o n d s

the s o l u b i l i t y

of

ions

Sm ~

/i0/.

to the up-

"

2120

5890

23.16 23.12 5.685

23D0

5.880

2296 0

Fig.

0.2

04

06

0.8 x ~ " ~ O

tO - i ~ x 0.8

0.6

0.4

0.2

14. T h e l a t t i c e p a r a m e t e r s of B a l _ x L n x F e l 2 0 1 9 s o l i d solutions, h o r i z o n t a l lines i n d i c a t e limits @-

It c a n be~

~-

-

Sm,

Ln:

O-

the

La,

Eu

if the size of s m a l l c a t i o n s

to p r e p a r e N d F e 2 + F e ~ + A I ~ + 0

6.5

see T a b l e

~.5 19

is

/ 1 1 / and

8.

to t r i v a l e n t h e a v y cations:

o b s e r v e d a n o m a l y in the l a t t i c e

p l a i n e d b y the p r e s e n c e

+

extended

series /12/,

us add the f o l l o w i n g r e m a r k s

- The

Nd~

T h u s it was p o s s i b l e

above all LnMgAIII019 Let

of the s o l u b i l i t y / 6 6 /

Pr~

however t substantially

also r e d u c e d .

0

of a c e r t a i n

parameters amount

of E u M g A I I I 0 1 9

can be ex-

of E u 2+ ions w h i c h are b i g g e r

than E u 3+ ones. -

The M-phase

o o n t a i n l n g Crd3+ ions is the last m e m b e r of the series.

Due

to

184

E. Polle~

the c o e x i s t e n c e correspond The

Bi 3+ h a v e

small

with

~-AI203

to the i d e a l

size

an i n t e r m e d i a t e

a n d c a n be l o c a t e d

Table

8. L a t t i c e ions

and GdAI03

phases

character.

They

in b o t h

parameters

of r a r e

of some

earths

/ii,

Lattice

21.988

PrMgAlll019

5.580

21.935

NdMgAlll019

5.577

21.902

SmMgAlll019

5.575

21.853

EuMgAlllO19

5.574

21.908

"GdMgAlll019"

5.57O

21.815

cations

meters

mation

effect,

heavy

Coulomb

b y the e x i s t e n c e various

in

the e l e c t r o n between

An i n f l u e n c e of

values

~ are

Ultimately of h e a v y

us n o t e

cations

monstrated

not

configurations the l a r g e

that

are

also

even y 3 +

by

sublattice

cases

23/.

2b 2 h a v e

their

of ionic

though

the l a t t i c e

cations

of

the c h a n g e s

even

the w h o l e

the e x i s t e n c e

ions

M + ions

that

Particularly

of M + and M 3+ h e a v y

the d i f f e r e n c e s

in some

from

of

It is

to the i n c r e a s e

to e x p l a i n

of Cs + a n d

lowest

a result one.

containing

us n o t i c e

considered.

radii

the

the s i m u l t a n e -

a static

series,

easy

by

probably

correspond

are

ionic

which

15 /22,

as 2b I a n d

than

9. L e t

is n o t

in the o x y g e n

support

in the Fig.

denoted

does

is d e m o n s t r a t e d

stabilized

let

see T a b l e

behaviour

where

sublattice

is m o r e

of L a 0 . 5 M 0 . s F e l 2 0 1 9

of the c o u p l i n g

the M - p h a s e

This

contribution,

dimensions,

parameters

contrast

in the o x y g e n

cations.

energy

Bao.6(K+Y3+)o.4FeI2019

= 1.19

sites

stabilized

of L a 0 . 5 C S o . s F e I 2 0 1 9 ,

15-20/.

tion

are

of t r i v a l e n t

f r o m N a + to Cs +. T h i s

a sharp

parameters

5.584

3+ 3+ Fe6.5AI4. 5

14/.

containing

LaMgAlll019

of the l a t t i c e

ferences

M-phases

/13,

12/

22.23

2+

does n o t

sufficiently

sites

5.687

significantly

radii

already 6-fold

c

ous p r e s e n c e

confirmed

and

a

NdFe

the c h a r g e

have

12-fold

Composition

Monovalent

its c o m p o s i t i o n

one.

dif-

there

is

para-

series

/8,

on the for-

of the o o m p o s l -

of the i o n i c

radii

rxi I =

/21/.

in the c h a r g e s long range

As a c o n s e q u e n c e

to be d i s t i n g u i s h e d .

eventually

ordering

two k i n d s

sizes

as it is de-

of t r i g o n a l

Crystal chemistry of magnetic oxides

Fig.

15. Long r a n g e o r d e r i n g O-oxygen

T a b l e 9. L a t t i e e

of heavy cations~

anions, @ -

11- 2bl,

185

MI, @ -

M2,

2b2

parameters

+ of some L a 0 . s M 0 . 5 F e I 2 0 1 9

M-phase Lattice

Composition

La0.sNa0.5Fel2019

4.2.

a

c

5.883

22.97

Configuration of outer electrons I. 39

2p 6

22 16

La0.5Ag0.SFel2019

5 85

22.85

1.53

La0.sTIo.sFeI2019

5.89

23.4

1.70

6s 2

17

La0.sCS0.sFel2019

5.566

21.99

1.88

5p 6

19

Small c a t i o n s of h o l e s

in the f r a m e s k e l e t o n

t r o l l e d b y the same f a c t o r s In o t h e r w o r d s

it d e p e n d s

of the h o l e s

is~ h o w e v e r ~

hexagonal

The most important

of the r e s p e c t i v e

more complicated,

a n d in some c a s e s

starting

ferrites

is con-

previously.

in a s i m i l a r w a y f r o m the one side on the dimen-

The situation Before

discussed

a n d f r o m the o t h e r side on the ionic r a d i i 2 v a l e n c y and

of o u t e r e l e c t r o n s

cation sublattices

of the o x y g e n s u b l a t t i c e

as in the case of s p i n e l s

configuration

them.

Ref.

M+

4d I0

The occupancy

sions

parameters

the d i s c u s s i o n

meanwhile

p a r t i c u l a r l y due to n u m b e r of

small energetical let us e m p h a s i z e

studied contained

small cations

cations.

differences that

between

the m a j o r i t y of

iron ions.

are l i s t e d in the s u b s e q u e n t

T a b l e i0.

186

E. Polle~

Table i0. Small cations entering the h e x a g o n a l ferrites

Atomic number

Cation

Configuration of o u t e r electrons

Divalent

Trivalent

Pentavalent

in 6-fold

12

Mg 2+

2p

0.57

0.72

25

Mn 2+

3d 5

0.66

O. 83

26

Fe 2+

3d 6

0.63

O.78

27

Co 2+

3d 7

0.58

O. 745

28

Ni 2+

3d 8

0.55

O.69

29

Cu 2+

3d 9

0.6o

0.73

3O

Zn 2+

0.60

0.7h

13

AI 3+

3d IO 6 2p

o. 39

0.535

21

So 3+

3p 6

O. 745

22

Ti 3+

3d 1

0.67

24

Cr 3+

3d 3

o . 615

25

Mn 3+

3d 4

o. 645

26

Fe 3+

3d 5

0.49

31

Ga3 +

3d I0

0.47

33

AS 3+

4s 2

0.58

y3+

4p 6

0.9

49

in 3+

4d 10

64

Gd 3+

5p 6 4f 7

0.94

65

Tb 3+

5p 6 4f 8

o .92

66

Dy 3+

5p 6 4f 9

o .91

67

No 3+

5p 6 4f IO

o .9o

68

Er 3+

5p 6 4f II

o. 89

69

Tm 3+

5p 6 4f 12

0.88

7o

yb 3+

5p 6 4f 13

0.87

71

Lu 3+

5p 6 4f 12

O. 86

83

Bi 3+

6s 2

1.o3

22

Ti 4+

3p 6

0.42

40

Zr 4+

4p 6

o .59

44

Ru 4+

4d 4

0.62

50

Sn 4+

4d I0

0.69

77

ir 4+

5d 5

0.625

Sb 5+

4d I0

0.6o

39

Tetravalent

6

Ionic radii, coordination 4-fold

51

0.62

0.62 0.62

0.8

o. 605

0.72

Cwstalchemistw ofmagneticoxides Zn2+ t Mn 2+. A m a r k e d p r e f e r e n c e coordinated

sites r e s u l t s

their placing

f r o m the e l e c t r o n

in the c r y s t a l l a t t i c e

problem becomes more complicated able.

of 40 s i t e s b e f o r e

such a behaviour

A~ expls.nation s e e m s g i v e n in the Fig. spective

sites~ Thus

ions f o r 4 - f o l d and determines Nevertheless

of t e t r a h e d r a l

(BaZn2Fe16027)

where a preferential

exist

to be c o m p r e h e n s i b l e

16. A d i s p l a c e m e n t

f r o m the cut of the W - s t r u c t u r e

of o x y g e n a n i o n s

surro~ndlng

u s u a l l y o n l y b y the s t e r i c effect~ interactions

the re-

is e n h a n c e d

of a n i o n s w i t h

these s i t e s are f a v o u r e d f o r r e l a t i v e l y

large

Zn 2+ and Mn 2+

@

Cut of the W - s t r u e t u r e ~ tions on the o x y g e n

influence

anions

is o b v i o u s l y m o r e i m p o r t a n t

of h e a v y ca-

surrounding

in

the h e a v y

S-t~ock

16.

oc-

too /25/.

cations.

Fig.

the

sites are a v a i l -

4f b y Zn 2+ ions was f o u n d / 2 4 / a n d i n d i c a t i o n s

the case of 4e s i t e s b y the C o u l o m b cations.

configurations

if two k i n d s

of B a M n 2 F I 6 0 2 7

provoked

and Mn2+(3dS)

of h e x a g o n a l f e r r i t e s .

It is the ease of B a Z n 2 W p h a s e

cupation about

of Z n 2 + ( 3 d l O )

187

4e sites

than the i n f l u e n c e

on o x y g e n s~nions s u r r o u n d i n g 4 f I ¥ sites.

E. PoIle~

188 The

steric

be s e e n

effect

6civ sites p = 0.62, pure

a random

Due

a strong among

compound

for

individual

/27/

octahedral

energy /28/

30/.

ces h a v e

The

ing corners

types

where

of Ni 2+ a n d a l s o

6CIV

sites

for Ba 2 Y phase

preferred,

with

can

the

the p r o b a b i l i t y exists

and 6CIV

phase.

Thus

plays

of o t h e r s

only

role

energy

are f a r t h e r

preference "excess"

to d e c r e a s e

for

the

those

apart.

cations

generally

distribution

by

the c h a r a c t e r

of

S-blocks

4f

the c o n t r i b u t i o n in the 4f 2 si-

S and T b l o c k s adjacent

inside

in

of the 6 g a n d

location

between octahedra

than

they have

concrete

is d e t e r m i n e d

in t h e i r

the a n i o n

divalent

their

to an

distribution

inside

the c a t i o n s

sites

an e f f o r t

a decisive

Gibbs

but

the r e p o r t e d

probably

and random

higher

3d 8 of Ni 2+ ions

coordination

of o c t a h e d r a l

positions

generally

of t e t r a h e d r a l

While

of Zn 2+ b e t w e e n

On the o t h e r h a n d

tes of M - p h a s e se /29,

slightly

configuration

6-fold

ferrite

of the C o u l o m b

occupation

M2Zn2Fe12022.

are

c a n be a t t r i b u t e d

sites.

on the

/26/.

to the e l e c t r o n

of the h e x a g o n a l W-phase

block

distribution

preference

the

cation

of Y - p h a s e

in the s p i n e l

strontium

Ni 2+"

of h e a v y

on the e x a m p l e

in Y - p h a -

by common

the o o t a h e d r a

Consequently

in the f o r m e r

fa-

shar-

the p l a c e m e n t

type

of s i t e s

is

favoured.

Co2+ t M g 2+,

Cu 2+.

of W s t r u c t u r e Relatively

small

Cu 2+ on the one in the s p i n e l s , ferrites. decisive

Then /34/.

tropy ions

are

rentially

with found

side

and

have

to be,

energy

however,

(Znl_xCUx)2W

solid

distributed

phase

taken

solutions

sites

occupancy from

where

dependence

temperatures

of o c t a h e d r a l

side,

energy

is by

of ions

treatment 1500K

slowly

temperature

is

aniso/25/. Cu 2+

and prefe-

down

to r o o m

and slow cooling sites

M g 2+,

existing

is i n f l u e n c e d

the m a g n e t i c

f r o m -~

cooled

31-33/.

of Co 2+,

in the h e x a g o n a l

migration

of

thermal

quenched

a high

also

S-blocks

27,

to the G i b b s

distribution

in t h o s e low

energies

account

on the

in the

/25,

on the o t h e r

term

temperatures

in s a m p l e s

quenched

into

cation

is the

at r e l a t i v e l y

the p r e f e r e n t i a l

the B a 2 M g 2 Y

high

the o c t a h e d r a l

Annealing

of Fe 3+ ions

of the e n t r o p y

example

sites

is r e p o r t e d

the p r e f e r e n t i a l

the r e s u l t i n g

at s u f f i c i e n t l y

occupy

also

between

this

the o c t a h e d r a l

of Y s t r u c t u r e

the c o n t r i b u t i o n

randomly

temperature. hances

differences

An i l l u s t r a t i v e

in the

to o c c u p y

in T - b l o c k s

Actually

the a n n e a l i n g possible.

A tendency

and

en-

b y M g 2+ ions.

the d i s t r i b u t i o n

Thus was

to b e B a 2 ( M g 02+ . 6 F e 33+ . 4 ) t e t r a ~M g 2+ 3+ 0 22 1.4 Fe 8.6]oota

which

was

changed

Cd 2+.

Likewise

as

after

annealing

at 9 7 3 K

to

/35/

Zn2+~

Cd 2+ ions

exhibit

a significant

preference

for

tetra-

C~alchemist~ of magneticoxides hedral

positions

following

tor determining tions tion

entering in

plete

the h o l e s

by

/36/.

of the r e s p e c t i v e occupy

only

the i o n i c sites for

Fe2+~

but

Fe 3+. T h e i r i.e.

/36-39/. hedral

As

u~willingness

tions

seems

sites

from (3d I0)

from

taneous

trigonal

Thus tions

energy sites

cations

4fVl

ions

instead

sites

side.

sites

parameters

(see T a b l e

of

role

dimensions

determining

the

of

dis-

w a s i n v e s t i g a t e d in a 2+ 3+ and BaFe~ Fe16027 phases Fe ~+ ions

with

I0)

one,

enter

while

octa-

Fe 3+ due

positions

is d e c i d i n g

the e x c e p t i o n

of

for mutual trigonal

si-

/40-45/. to o c c u p y

the f i v e - f o l d of h e a v y

of the M e - 0 leads

more

u~stable. lying

posi-

surrounding

to the b o n d

pronounced

distances.

to an i n c r e a s e

become

coordinated

cations

of c o v a l e n c y

It is o b v i o u s l y

this

of G a 3+

than

for

Consequently

simul-

of PV c Q n t r i b u t i o n

One

can

close

expect

that

to

the

to the p o s i t i o n s

of

sensible.

2b s u b l a t t i c e

hexagallate

to x = 1 0 . 3 8 by

sizes

tetrahedral

in the R - b l o c k s

enter

of p u r e

is s u g g e s t e d

an i m p o r t a n t

absolute

to m a g n e t i t e ,

the s i z e s

effects

1.31Ba0.6Ga203

corresponds

ions with

the m o s t

do n o t

of C u 2+ ions,

at the o c t a h e d r a l

systems,

6g in the l a t t e r

is r a n d o m

the s t r u c t u r e

be

where

lattice

Fig.

and will

gallium

composition

4fvi

and

and

3d 5 p r e f e r

to an i n c r e a s e

of b o t h

in

rates

sublattioes

and a contribution

the o t h e r

leads

influence

the G i b b s

side

a part

only

play

LaFel2019

Fe 3+ ions

of g a l l i u m

the o n e

the

ions

case

which

to be c o n n e c t e d

F e 3 + ( 3 d 5) a n d

heavy

with

cations

is i n c o m -

a n d x = 0.5

Zn 2+ a n d Cd 2+ c a t i o n s

is p r e s e n t

their

analogically

configuration

similarity

at l e a s t

does n o t

among

iron

in the f o r m e r

of b o t h

latter

both

ca-

the s u b s t i t u -

is in the o c c u p a t i o n

in the f o r m e r

between

(M-phase) a n d 2d ( V - p h a s e ) ,

tes 2b

ions

only

one c a n a s s u m e ,

G a 3+. T h e i r

to that

Zn-series

fac-

i n o u r c a s e o f ( C d 2 + ) t e t r a - 0 - ( C u 2 + ) o c t a.

distribution

electron

replacing

i.e.

in the

as in the s p i n e l

structure

the r e l a t i o n

containing

2a s i t e s

their

ber

also

Due

Further

the l a r g e s t

and Ba2(CUl_xCdx)2Fe12022

of Fe 3+ ions,

like

they are

sublattice.

the d i f f e r e n c e

in the

that

Then,

the

of

of

configuration.

dimensionj

of X = 0.7

While

sites than

(Mel)A-O-(Me2)B,

"pure",

The

reason

tetrahedral

of the S - b l o c k s .

tances

to

The

positions.

the s t a b i l i t y

3d I0 e l e c t r o n

in the o x y g e n

the v a l u e s

radii bigger

the c a t i o n s

the

is t h e i r

Ba2(Znl_xCdx)2Fe12022

the s e r i e s

and limited

the C u - s e r i e s

from

their behaviour

189

for BaFel2_xGax019

BaGal2019

another

arises

/46/

and for Pb-series

/47/.

0nly

pure

the c h a n g e

on c o m p o s i t i o n

SrGalS019

of the s l o p e

of

in the P b F e 1 2 _ x G a x 0 1 9

where

exists. the

solid

structure

the

the last

mem-

Sensibility

dependence

series

solu-

of

of

of

the

at x , ~ 3

(see

17).

A I 3+. T h e y

have

can a s s u m e

a preference

the S - R a n d

a more

ionic for

S-T i n t e r f a c e s

character octahedral

(see T a b l e

than

the Fe 3+ a n d G a 3+ ions.

sites, i).

On

particularly the o t h e r h a n d

Then

in S - b l o c k s

one

and

the o c c u p a n c y

in of

190

E. Pollert

23.12

o[ 1 23.08

23.0~

r-

23.00

587

2296

~85

2292

5.83 I

0 2 12-(W xlO Fig.

17. D e p e n d e n c e

I

I

I

~, 8

6 6

8 A

I

10 x't-~-" 12 2 0

of the l a t t i c e p a r a m e t e r s

sition in the P b F e l 2 _ x G a x 0 1 9 Othe o c t a h e d r a l undesirable

a,

e-

c

sites

be s o m e w h a t

of the C o u l o m b

with magnitudes

The

dependence

represented the r e g i o n

leads

to an

and it is less favour-

but the o r i g i n of this b e h a v i o u r

A 1 3 + ions h a v e

seems

to

too s m a l l i o n i c r a d i i in c o m p a r i s o n

of Fe 3+ and Ba 2+ cations.

of the s u b s t i t u t i o n

in the Fig.

18 p o i n t s

of 6 - - = x ~ = 7 . 2 .

ference between

ootahedra with common faces energy contribution

case of G a 3+ ions a l o w t e n d e n c y to o c c u p y

is r e p o r t e d /45-52/}

different}

on c o m p o -

solid solutions,

/l/.

sites in c o o r d i n a t i o n

increase

ed. S i m i l a r l y as in the p r e v i o u s trigonal

5.89

at 2b sites of the B a F e l 2 _ x A l x 0 1 9 to the e x i s t e n c e

The reason

the d i m e n s i o n s

is p r o b a b l y

of a m i s c i b i l i t y the r e l a t i v e l y

of A 1 3 + and Fe 3+ cations~

series g a p in

large

dif-

c a u s i n g l o c a l dis-

tortions. The

difference

between

f o r the e x i s t e n c e embed

(BaAI03)-

layers

be too small. T h u s

in

instead

proximate compositions see also latter. In3+t

the i o n i c r a d i i of AI 3+ and Ba 2+ c a t i o n s

of c o m p o s i t i o n s

close

to x ~ 1 2 .

(All1016)+ m a t r i x b e c a u s e of i d e a l B a A I I 2 0 1 9

Ba0.82AII2018.82

So 3+. T h e s u b s t i t u t i o n

is d e c i d i n g

It is n o t p o s s i b l e

to

the Ba-0 d i s t a n c e s w o u l d

bariumhexaaluminates

and B a l . 3 1 A I I 2 0 1 9 . 3 1

of the ap-

are f o r m e d /46/,

of I n 3 + ( 4 d I0) a n d $ 0 3 + ( 3 p 6) f o r Fe 3+ was s t u d i e d

Crystal chemistry of magnetic oxides

191

occupation I

I , I

1.0

0.8 O.

0.6

>.

0.4

02

0 Fig.

I

I

2

~;

I

6

T ?

8

T

10

x

18. N u m b e r of Fe 3+ ions in 2b s u b l a t t i c e formula

of B a F e l 2 _ x A l x O l 9

a function

of X

12 p e r unit

solid solutions

as

/49/

in M - p h a s e s BaFel~ M e 3 + O _ ^ i n the r a n g e of 0 ~ x ~ = 3 . 4 and in W - p h a s e s . 2+~ ~ 3+~ ~ - x ~ X 2 + ± ~ ~ 2+ Ni2+ ~ a M e 2 F e l 6 _ x M e x U27 , Me = zn , in the r a n g e of 0 < x _ _ ~ 4 . 5 (45, 48-64/. O b v i o u s l y it leads to an i n c r e a s e of the l a t t i c e p a r a m e t e r s and f o r

3+

3+

Baln 3.4Fe8.6019

it was f o u n d a = 6 . 0 0 ~, c = 23.79 ~. T h e y e x h i b i t

rence for R-blocks where

t h e y o c c u p y both,

sites with a slightly lower occupation

This f i n d i n g

is r a t h e r s u r p r i s i n g

Particularly

this a p p l i e s

preference

oetahedral

a prefe-

4fvi a n d t r i g o n a l

2b

rate f o r the l a t t e r ones.

f r o m the c r y s t a l l o e h e m i e a l

point

of view.

to the case of In 3+ ions w h e r e one w o u l d e x p e c t a

f o r the t e t r a h e d r a l

sites,

eventually a collapse

of the s t r u c t u r e

like in the s i m i l a r s p i n e l s y s t e m s /65/. T h e s t a b i l i t y is p r o b a b l y a t t a i n e d b y the d e f o r m a t i o n

of the r e l e v a n t

due to a n i n f l u e n c e

C r 3+. T h e e f f e c t series

of the s u b s t i t u t i o n

electron

a significant

configuration

gradually

2a;

12K,

not

the

tetrahedral

enter

lutions

is

4fvi

0tx_____10.

sites ones. Let

(see

With

the

that

is a c c o m p a n i e d b y the s t r o n g d i s t o r t i o n

a u t h o r s /66-69/. for

19)

and

concentration for

homogeneity presence

As one can expeot~

oetahedral positions

increasing

Fig.

Thus

us note

trigonal bipyramids)

of C r 3+ f o r Fe 3+ ions in M C r x F e l 2 _ x O l 9

preference

3d 3.

(octahedra,

h e a v y cations.

(M = St, Ba) w a s s t u d i e d b y s e v e r a l

Cr 3 @ ions e x h i b i t their

polyhedra

of s u r r o u n d i n g s

of

x =~9

the

range C r 3+ a t

due t o

they

of

occupy

2b sites these

the

trigonal

of t h e i r environment /68/.

b,~t

solid

do so-

sites

192

E. Polle~

Mn 3+. ....

It is w e l l

known

that

be p l a c e d

in o e t a h e d r a l

ic s t a t e

can be r e m o v e d

Teller

effect).

spinels

The

the Mn 3+ ions

sites

by lowering

problem

was

or p e r o v s k i t e s w but

the B a F e l 2 _ x M n x O l 9

series

As f o l l o w s

from

to g r a d u a l

increase

rameter.

This

the Fig.

Mn 3+ ions 19

this

were

is r a t h e r

system

a strong

of

degeneracy

the s y m m e t r y

extensively

only recently

of

studied

their

substituted

substitution

leads

and seems

ferrites

decrease

like

e.g.

where /70,

in

71/.

of O - - ~ x - ' = 8 of the c pa-

to i n d i c a t e

distortion

(Jahn-

materials,

f o r Fe 3+ ions

to

electron-

surrounding

in the r a n g e

and simultaneous

surprising

tendency

their

in v a r i o u s

in the h e x a g o n a l

to the r e s u l t i n g

contribution

in the p e r o v s k i t e s

(3d 4) e x h i b i t

the o r b i t a l

of the a p a r a m e t e r

finding

of an a d d i t i o n a l

where

the existence

that

observed

/TR/.

o~ 5,9& 232O

23.18 592 23.16

23.16 5.90 23.12

23.~ 5.88 0

Fig.

1

19.

2

3

Dependence sition • - a,

in

limit

firms not

of the s e r i e s

the m e n t i o n e d

enter

of the l a t t i c e

O-

c /70/,

ordering to that

of

at the

this

and five-fold

with

solid

a,

on c o m p o -

solutions,

A - c, E.

Pollert,

BaFe3Mu9019

for octahedral sites.

The

to the p o s s i b i l i t y cooperative

triolinio

x

results

coordinated

leads

MnO 6 oetahedra,

structure

8

to the c o m p o s i t i o n

of Mn 3+ ions

composition

distorted

a new crystal

O-

7

parameters

unpublished

corresponds

preference

tetrahedral

of Mn 3+ ions

6

the Bal2_xYanxOl9

L. M a t ~ j k o v f ,

The

5

&

high

con-

t h e y do

concentration

of a l o n g r a n g e

Jahn-Teller

symmetry

which

positions~

is formed.

effect.

Due

Cwstalchemistw ofmagneticoxides Rare

e a r t h cations.

rare e a r t h c a t i o n s decreases suitable amounts

As it was a l r e a d y shown, deoreases~

see Fig.

their capability

of G d 3+, He 3+ a n d D y 3+ c a t i o n s

sublattioes

while

Tetravalent

cations.

Tetr~valent

to a t t a i n

of rare

in /73/,

into

small

the 2a and 1 2 K

p r e f e r 2b and 4 f v i p o s i t i o n s .

of s u i t a b l e radii,

into the h e x a g o n a l

the e l e c t r o n e u t r a l i t y

earth cations become

can b e i n t r o d u c e d

cations

the size of

the o x y g e n a n i o n s

T h u s as w a s r e p o r t e d

the s m a l l e r Y b 3+ c a t i o n s

Sn 4+, T i 4+ can b e i n t r o d u c e d

14, w h e n

to r e p l a c e

too. On the o t h e r h a n d the d i m e n s i o n s to o c c u p y c a t i o n s u b l a t t i o e s .

193

simultaneous

ferrite

presence

like Ir 4+ /74/,

l a t t i c e but in o r d e r

of d i v a l e n t

cations

is

required.

The examples pairs

are R - p h a s e s

BaFe4Sno011

/ 7 5 / and B a F e 4 T i 2 0 1 1

of Fe 2+ - Sn 4+ and Fe 2+ - T i 4+ cations.

/76-78/ containing

The distribution

of c a t i o n s

the l a t t e r c o m p o u n d was f o u n d to b e in the a ~ r e e m e n t w i t h the e x p e c t e d i.e. T i 4+ c a t i o n s sitions between iron ions

occupy ootahedral

the R - b l o c k s

( p r o b a b l y Fe3+).

2d [

while

sites w i t h a s l i g h t p r e f e r e n c e trigonal

in

one,

f o r 6g po-

2d s i t e s are o n l y o c c u p i e d b y

T h e n it csus be e x p r e s s e d b y the f o r m u l a

el.lTi0.9] 4e [

el.gTil.1]6g

of Me 2+ + Me 4+ p a i r s f o r F e 3 + in M M e 2+ Me 4+ Fe 3+ .....0 solid ~x x h l ~ - ~ x A~ s t u d i e d p a r t i c u l a r l y in the case of Me -+ ÷ T i -+ couples. U s u a l -

The substitution s o l u t i o n s was ly, h o w e v e r ,

their concentrations

p l e t e s e r i e s are r e p o r t e d

do n o t e x c e e d v a l u e s

f o r BaCo~+Ti~+Fel2_2xOlg~

of x ' ~ 2

/79-85/.

Com-

/ 8 6 / and

BaMg~+Ti~+Fel2_2xOl9A~ / 8 7 / s o l i d solutions, Replacing

of iron ions lead~ at f i r s t

b y Co 2+ e n d T i 4+ cations. ions are s u b s t i t u t e d

T~en

randomly while

p l a c e d o n l y at h i g h d e g r e e s w i t h the d i s t r i b u t i o n 4+

4+

coordinated

in t r i g o n a l

This behaviour

in the M - p h a s e

2+

of 4 f l V and 4 f V l sites

ootahedrally

the iron ions

of s u b s t i t u t i o n .

of c a t i o n s

2+

to the o c c u p a n c y

the r e m a i n i n g

BaTi6M~6019

[Ti 4+ M 2+ I

iron

sites are re-

seems

to c o n t r a s t

/88/:

r. 2+I

Ba [Ti3.7 8MgS.22]12K [Ti098M 0 02]2a~ 0.6 gl.4]4fVi[Mg2]4fly 4+

2+

The distribution

found confirmed

1 2 K a n d 2a p r e s u m e d contribution.

Finally, that

as a c o n s e q u e n c e

of T i 4+ in o e t a h e d r a l

of an effort

to l o w e r the C o u l o m b

On the o t h e r h a n d f r o m this p o i n t of v i e w p r e s e n c e

tions in t r i g o n a l

note

the p r e f e r e n c e

before

sites energy

of T i 4+ ca-

sites is u n e x p e c t e d .

closing

the p r e s e n c e

N b 5+, Sb 5+ in h e x a g o n a l

the d i s c u s s i o n

concerning

of s m a l l c o n c e n t r a t i o n s

the s m a l l c a t i o n s

of p e n t a v a l e n t

f e r r i t e p h a s e s w a s also r e p o r t e d /82,

let us

c a t i o n s V 5+, 89/.

194

E. Polle~

5.

5.1.

S.tackin~

Due

to the

the as

of

Sequential

always

occur

the

the

into

sequence

and

structural also

faults.

Three

caused

does

types

intergrown

by

not

small

structures

a transfer

can

be

change

the

the

easily

i.e.

of arise

sequential

distinguished.

of b l o c k s

locations.

among

differences

of f a u l t s ,

phases

to o t h e r

differences

only

defect

intermediate

and

are

as

to s u p p o s e

sequences

3 can

crystal. more

of d e f e c t s to b e

M Y M Y 6 M Y M Y 4 in

sequence

sequences.

the

becomes

crystals

There

is

can

This

from

their

type

stoiohiometry

regular

of f a u l t s

and

the

unit

must cell

defect

example

can

be

is

the

are

the

to

3 in

result

regular

the

from

and

the

close into above

to s e p a r a t e

rhombohedral

of

interruption

M6Y19

the

phase

the

arrangement

to p u r e the

by

to f o r m

sequence

described

units

by

least

with

the

The tend

extent again

deficiency

inclusion the

units

structure

region.

a small

of

by

the

the

(which

of a l o c a l

as a t w i n

M8YI8

extraneous

is c h a n g e d .

sequences

at

of

interrupted,

Y phase,

matrix

M u~its

phase

insertion are

isolated

of

random

introduced

alternatively

MYMY 5 or

the

stoichiometry

inclusions

the

mentioned

structure

sequences

a composition

i.e.

matrix

examples.

be

a tendency

...YYYMYMYYY...,

as

disordered

regularly)

with

cations

serve

They

vary

may

the

MYMY3MY4MYsMY3My

Originally

or less

ordered

heavy

As

They

in p a i r s

regular

Irregular

the

stacking sequences

original

MYMY4MY3MYsMY3MY

For

STRUCTURES

of a p h a s e .

Disordered of

the

faults.

in

RELATED

as w e l l

is p o s s i b l e

Consequently

irregular

places

size

it

energie.

a result

faults~

compositional

phases

Gibbs

AND

faults

small

individual

DEFECTS

of

of M - u n i t s .

type

a single

Y

unit.

Thus

plane.

stacking

MX~Y4MV~4M~~ which

can

be

considered

as p e r i o d i c a l l y

twin

faulted

MYMY 4 structure.

plane

...Y4MYMY4MYMY4MYMYYMYYMYMY4MYMY4MYMY4 An i n s e r t i o n in

the

M-units, already

of Y - u n i t s

crystal. even

The

within

resulting

and

odd~

discussed.

Let

in

the

us n o t e

M-matrix structural separated that

for

leads

to an

properties parts even

of

the

numbers

excess

of h e a v y

depend

on n u m b e r s

original of M - u n i t s

cations of

sequence the

as w a s

separated

Cwstalchemist W of magneticoxides parts

are related

alternatively

The

same

effect

S-blocks

by a translation

described

on

(see M n S

deficiency

of p h a s e s .

tually very

close~

scopic

members

sense

along sudden

the M - m a t r i x

the s t r u c t u r e s

are no

obstacles

direction from

one

is an e x a m p l e

tions:

from

sequence where

the i d e a l

improper

lattice

ratio

single

can

forming ready

of

in the m a c r o -

in d i f f e r e n t

The

are mu-

particularly

crystal"

a change

change

was

phases

intergrowth,

to the other.

sections

c a n be s h a r p w i t h

transition

a

f r o m M 2 Y 8 to

of the c o m p o s i t i o n

from

found.

/i/.

suppose

that

the f r a m e

mentioned~

quences.

Then

replacement

by

tices~

see T a b l e

to the M - t y p e

of the

where

siderable

with

from

(units)

contribu-

anions

metal

ions

in the

control-

have

barium

the s t a c k i n g

deviation

metal

sequence

from

can

equilibria

cations

The

character. varying

stacking

selead

to

chains

Ba0.nFe203

is atsublat-

containing

structure

is c l o s e

(n = 4.22)

to

~ - F e z O 3 the Y" unit conta±ns

[]2/3__ /

is p a r t i c u l a r l y

if 2 x F e 3+ + x ~

al-

explained

in the c a t i o n

from M2¥ ~

Fe~/J~u

are p r e s e n t

c a n be

electroneutrality

Their

of

sublattiee as it was

in the c r y s t a l s

and vacancies

the s t o i c h i o m e t r i c

occur

found

magnetoplumbite

In analog7 to defect spinel

of the s o l i d - g a s

the r e g u l a r

hexaferrites

a similar

as an e x a m p l e

and~

composition

in

respectively.

Fe 2+ ions

serve

on the o x y g e n

of l e a d

in the r e g u l a r

can

is e x c l u d e d

the i d e a l

or an e x c e s s

of b o t h

ions

transition

structure

two p o s s i b l e to o x y g e n

transition

series

b l o c k S" of the c o m p o s i t i o n (Fe3+)2 one (Fe3+)2 ~ ~e 3+-~e 2+ 2 08 /90/.

An influence

from

valencies

of v a c a n c i e s

blocks

ii. M e t a s t a b l e

iron

H20Y ~ (n = 5.56).

originate

fixed

the s t r u c t u r e

S and T blocks

the p r e s e n c e

trivalent

of

the d e v i a t i o n s

a deficiency

by

crystal

the e x i s t e n c e

skeleton

of the R - b l o c k s

...SRS~R...

with

of the v a l e n c i e s

of e x t r a n e o u s

tained

vacant normal

stoichiometry

of the P b F e l 2 _ x G a x 0 1 9

case

b y the p r e s e n c e

ses~

to a

equilibria.

crystals

the f o r m e r

only

Such

the s h a r p

of c a t i o n s

and variations

led by solid-gas

One

of

it leads

Nonstoiohiometry

Deviations

The

can be

an i n s e r t i o n

of the i n d i v i d u a l

to the

of the c-axis.

B a l s Z n l 6 F e l 2 0 0 2 1 ~ to B a 1 4 Z n 1 2 F e 9 6 0 1 7 0 5.2.

causes

to the s t o i c h i o m e t r y

the M Y series. T h e n a " s i n g l e p r v a r y in c o m p o s i t i o n a n d s t r u c t u r e

trau~sition

M2Y 6 phases

of

arrangements

of a s h e a r plane.

of

might

the c o m m o n

the r e s u l t i n g

in the c r y s t a l .

Since

there

that

With regard

cations

Inter~rowth

so

to the i n t r o d u c t i o n

the s t r u c t u r e series).

of h e a v y

different

as due

195

in

08 i n s t e a d

of the

remarkable

two v a l e n c i e s .

composition

without

([] = metal

cation

f o r pha-

Then

a con-

a change vacancy)

of is

196

E. Polle~

substituted

for

3xMe 2+.

B a F e 22+ _ 3 x [ ] x F e 1 6 3+ +2x027 per formula that

unit

can v a r y

the i r o n - d e f i c i e n t

annealing

to M a n d

diffusion

of i r o n

subsequent,

5.3.

of a g r e a t

phases.

The

process

without slower,

destruction diffusion

of h e x a g o n a l

number

all

in

the n u m b e r It was

and d e c o m p o s e is c o n t r o l l e d

the case

of

of Fe 2+ ions

found,

however,

after

long-time

by

two m e c h a n i s m s ,

of the c l o s e - p a c k e d

of l a r g e

several

examples.

As it was

of o u r

already

suggested,

on the s t a b i l i t y small

ferrites

of r e l a t e d

only

structure

and

Ba 2+ ions.

leads

structures.

discussion

the size

and

the s t r u c t u r e

Their

cations

ferrite

becomes

unstable

to the exist-

description

consequently

of h e a v y

of the h e x a g o n a l

simultaneously

we w i l l

has

would

exceed

briefly

an i m p o r t a n t

structure.

If

and a t r e n d

men-

in-

they are

too

to a n o t h e r

ar-

appears.

Monovalent

cations

case.

c a n be p r e s e n t

They

above

of 0 ~ y R 5 2 .

unstable

tion

or too

studied

are

the e x t e n t

large

was

y = 2 - 3 x , i.e.

structures

versatility

rangement

where

in the r a n g e

obviously

fluence

behaviour

W-phases

Fe203 ions

obviously

Related

A large ence

This

/91-83/

of a l k a l i n e

the s i t u a t i o n

is s i m i l a r )

the ~ - a l u m i n a

structure

metals

can

in the M - t y p e only

serve

phase

in a l i m i t e d

is f a v o u r e d ,

as an e x a m p l e

concentration

see Fig.

20.

structures type

cations,

of the i n t e r m e d i a t e

of the M - p h a s e (b). O -

I - 2b, @

oxygen

type

ferrites

and formation

b

Configuration

mina

the f o r m e r

20.

o

Fig.

of

(for o t h e r h e x a g o n a l

layers

in the

(a) a~nd ~ - a l u -

anions, @ - h e a v y

4fvz, @- 4fly

of

Crystal chemistry of magnetic oxides

H

C~

0

0

~-I

•.~

O

I)

~1

~,

0

0

0

0

0

0

0

0

0

0

0

0

O

',0

.~"

¢~

O~

['~

0

0 ~,

+

o

0

~

0 +

O

+

O

O

0

+

•~

.)

0

197



O

O

O

..I-





,-t O M 14 I

0

0 0

4~ O ~

O "H O

P~

,-t

,"-I

u'~

,.-4

O

i;~

o~

00 0

O

O 4~ 0 0 0

0

v-[

00

c'~ _[

-~" ,--I

Ox

0

ol

.~"

e~

,-I

0

198

E Polle~

T h e c a u s e is obvious:

occupation

of the l a y e r b e t w e e n

the s p i n e l slices b y

o n l y one h e a v y c a t i o n ~ n d one oA-ygen a n i o n is m o r e a d v a n t a g e o u s ric r e a s o n s

than the a r r a m g e m e n t

e x i s t i n g in the M-phase.

structure

f r o m the ste-

T h e r e a s o n f o r the

existence

of ~ - a l u m i n a

aluminate termediate

Bao.75AIIIOIT.25 is p r o b a b l y the same. T h e c o n f i g u r a t i o n of the inl a y e r in a ~ - a l , l m ~ n a

Ba 2+ ion than that in an M - t y p e charge

Due to that,

One of the c o m p o s i t i o n (0AIII017)3-.

affords

structure.

To a t t a i n

----.

i I

Another point

of h a l f unit cells

throughout

?

II

I

is the

divalent

must be c o n s i d e r e d .

b o t h types m u s t c o m b i n e

in the

the c r y s t a l /94-97/.

~_

I

---- -

I

;

%~J

to be n o t i c e d

phase containing

a n d the o t h e r one of the c o m p o s i t i o n

the e l e c t r o n e u t r a l i t y

.

I

more space f o r the large

note that the l a c k of s u p e r s t r u c t u r e r e f l e c t i o n s i n d i c a t e s

3:1. Let us

I

two k i n d s

(BaAIIIOI7)+

their random distribution

: * :i :

structure

compensation m e c h a n i s m in this ~ - a l u m i n a

B a 2+ cation.

ratio

in the case of the a l r e a d y m e n t i o n e d h e x a -

ill"

. .

.

.

.

',A

"

I

.

I

I ~,jJ--

®

,

-- "

I

®

®

Fig.

21. A m o d e l f o r the s t r u c t u r e p h a s e /99/. in h e x a g o n a l

Relation ferrites

of 1 . 3 1 B a O . 6 M e 2 0 3

between

a n d B a 3 0 3 and B a 4 0 4 layers lines)

respectively.

the o c c u p a t i o n ,

I, 3, 5, 6 are empty,

se s t r u c t u r a l

structures,

1-6 are

B a 4 0 4 layer: positions

more complex for Ba-rich phases

8/id # - a l u m i / l a

types.

positions

98/.

posi-

2, 4 oc-

See also Figs.

( B a l . 3 1 M e 1 2 0 1 9 . 3 1 ) , w h e r e Me = A I 3+, Oa 3+ /95, rity with M-type

s h o w the change of

B a 3 0 3 layer:

c u p i e d b y h e a v y cations. The situation becomes

(indicated by full

Arrows

o c c u p i e d b y o x y g e n anions, tions

the B a M e O 3 l a y e r

( i n d i c a t e d b y d a s h e d lines)

22 and 23.

like 1 . 3 1 B a 0 . 6 M e 2 0 3

In spite of their s i m i l a -

t h e y do n o t b e l o n g

to any of the-

Crystal chemistry of magnetic oxides

199

Fig. 22. A model for the structure of 1.31BaO.6Me203 phase (He = AI, Ga). Sequence of the Me Ba303 Me 3 012 layers. - oxygen anions, @ - h e a v y dations I small cations in tetrahedral sites.

[email protected] -

Electron diffraction study showed rhombohedral lattice having unit cell in comparison with the original magnotoplumbite cell a ~ x a ~ enlarged and containing two types of "Ba0" layers} their deviation see Fig. 21. Thus a structural model including Ba303 and Ba404 layers with the following sequence of layers in the basic unit was proposed /99/j IBa3031 Me31 0121 Me9 10121 Me81 0121Melol 0121 Me21Ba4041 Me21 i

1012 IMelol 012 IMe8 I012 IMe9 I0121 Me3 IBa3031 m

Let us note that in the usual hexagonal desoriptlon the period spans over 30 layers which corresponds to the composition (Ba70640103) . Detailed arrangem e n t of the Ba-layers in the structure is shown in Figs. 22 and 23.

200

E. Pollert

Fig. 23 . A model for the structure of 1.31BaO.6Me203 phase

(Me = il, Ga). Sequence of the

[ 0121 Me2 [Ba404l Me210121 lay ers. - oxygen anions, @ heavy cations,

~

-

@-

small cations in tetrahedral sites~ small cations in octahedmal sites ACKNOWLEDGEMENT

The author wishes to express his gratitude to dr. C. Nov~k and dr. K. Z~v~ta for helpful discussions and critical reading of the manuscript and to ing. E. Kuzmi6ov~ for kind assistance in literature searching. REFERENCES Literature used in the parts 2 and 5.1 not quoted in the text: J. Smlt, H.P.J. Wljn, Ferrltes, Phlllps" Technical Llbrary (1959) W.D. Townes, J.H. Fang A.J. Perrotta, Zeit. fur Krlst. 12~, 437 (1967) R.0. Savage, A. Tauber J . Am. Ceram. S o c . 4 7 , 13 (1964) R.0. Savage, A. Tauber

Mat. R o s . B u l l .

J.A. Kohn, D.W. Eokart

Zeit. fur Krist. ll~, 454 (1964)

J.A. Kohn, D.W. Eckart

J. Appl. Phys. 35, 968 (1964) J. Appl. Phys. 36, 1171 (1965) Am. Miner. 50, 1371 (1965)

J.A. Kohn, D.W. Eokart J.A. Kohn, D.W. Eokart

~,

469

(1967)

Cw=alchemi~w ~ magneticoxides J.A. Kohn, D.W. Eokart,

Zeit. f~r Krist. 124, 69

201=

(1967)

D.W. Eokart, J.A. Kohn, Zeit. f~r Krist. 125, 130 (1967) J.A. Kohn w D.W. Eokart, C.F. Cook, Jr.~ Mat. Res. Bull. ~, 55 (1967) J.A. Kohn, D.W. Eokart, C.F. Cook, Jr., Science 172, 519 (1971) C.F. Cook, Jr., J. Appl. Phys. 38, 2488 (1967) J. Van Landuyt, S. Amelinokx, J.A. Kohn, D.W. Eokart, Mat. Res. Bull. ~, 339

(1973) J. Van Landuyt,

S. Amellnokx,

J.A. Kohn, D.W. Eokart, Mat. Res. Bull. ~,

i173 (1973) J. Van Ls~uduytm

S. Amellnokx~

J.A. Kohn, D.W. Eekart~ J. Sol. St. Chem. ~,

103 (1974) J.S. Anderson, /i/

J.L. Hutohlson,

Cont. Phys. 16, 443 (1975)

E. Pollert, M. Nevgiva, L. Mat~jkov~,

J. Nov~k, Mat. Res. Bull. 16,

1499 (1981) /2/ /3/ /4/ /5/

N.N. Sirota, M. Sehieber, N. Iohinose, G. Asti, M. Mag. Mat.

V.I. Bondar, US patent No K. Kurihara, Carbueioohio,

Dokl. Ak. Nauk B S S R 2 1 , 507 (1977) 1.932.502, 1965 (Filed 1961) J. Phys. See. Jap. 18, 1700 (1963) A. Deriu, E. Lueehini, G. Slokar, J. Mag.

2o, 44 (1980)

/6/

F.K. Lotgering,

/7/

A. Desehamps,

M.A.H. Huyberts,

F. Bertaut,

Sol. St. Commun. 34, 49 (1980)

Cempt. Rend. 244, 3069

(1957)

/8/ /9/ /i0/

M. Drofenlk, B. Hanzel, A. Moljk, J. Mat. Sol. ~, 924 (1973) A.M. Van Diepen, F.K. Lotgering, J. Phys. Chem. Sol. 35, 1641 (1974) E. Pollert, L. Mat~jkov~, Cryst. Research and Teehnol. 16, K53 (1981)

/ii/ /12/ /13/

U. Lehmann, H. M~ller-Busehbaum, Z. anorg, allg. Chem. 486, 45 (1982) 0. Saber, k.M. Lejus, Mat. Res. Bull. 16, 1325 (1981) P.P. Kiri~ok, N.B. Voronlna, 0.F. Bere~ak, Izv. vys. uoeb. zav., SeN.

/14/

/15/ /16/

A. Grill, Int. J. Magn. ~, 173 (1974) R.N. Summergrad, E. Banks, J. Phys. Chem. Sol. ~, 312 (1957) K.K. Laroia, A.P.B. Sinha~ Indian J. Pure Appl. Phys. i, 215

/17/ /18/ /19/

K.K. Laroia, Indian J. Pure Appl. Phys. i, 396 (1963) A.I. Mitsoh, phys. st. sol. ~, 137 (1974) P.E.D. Morgan, D.R. Clarke, C.M. Jantzen, A.B. HarkeN,

Fiz. 27, 116

(1984)

(1965)

J. Amer. Cer.

see. 64, 249 (198l) /20/ /21/ /22/

J.A. Mamaluj, L.P. 01ohovik, Sol. St. Phys. 24, ii, 3431 J.A. Mamaluj, L.P. 01ohovik, Ukr. phys. j. 24, 906 (1979) J.A. Mamaluj~ L.P. 01ohovik, L.F. Teheteherskaja, Ukr. phys.

j. 26,

562 (198l)

/23/ /24/

J.A. Mamaluj, L.P. Olehovik, Ukr. phys. J. 24, 906 (1979) M.N. Desehizeaux-Cheruy, M. Vallet-Regi, J. Sol. St. Chem. 57, 234

/25/

T. Besagni, A. Deriu, F. Lieei,

(lgs~) 79l (1983)

S. Rinaldi,

J. Mag. Mag. Mat. 31-~4,

202

E. Polle~

/26/

A. Deriu, F. Licci, (1981)

S. Rinaldi, T. Besagni, J. Mag. Mag. Mat. 22, 257

/27/

T. Besagni, A. Deriu, F. Lioei, L. Pareti, 17, 2636 (1981)

/28/

J.G. Rensen, J.A. Sehulkess,

S. Rinaldi,

J.S. van Wieringen,

IEEE Trans. Mag.

J. de Phys. Suppl.

32,

ci-925 (1971) /29/

I.I. Petters, L.N. Grigorjeva, B.N. Jermakov, Ser. Neorg. Mater. ~, 828 (1971)

Izv. Akad. Nauk SSSR,

/30/ /31/

V.N. Avramenko, E.V. Sinjakov, ibid. ~, 1264 (1969) G. Albanese, A. Deriu, F. Lieei, S. Rinaldi, IEEE Trans. Mag. 14, 710

/32/ /33/

G. Albanese, G. Asti, IEEE Trans. Hag. ~, 158 (1970) T.A. C h i m i c , V . F . B e l o v , M.N. S i p k o , E.V. K o r n e j e v , S o l .

(1978) S t . P h y s . 1_~1, 2093 (1969) /34/ A. Navrotska, 0.J. Kleppa, J. Inorg. Nucl. Chem. 29, 2701 (1967) /35/ M.A. Vinnik, A.P. Erastova, J.G. Saksonov, Sol. St. Phys. ~, 269 (1966) /36a/ A. Deriu, F. Lioci, S. Rinaldi, T. Besagni, J. Mag. Mag. Mat. l~-lS,

1445 (1980) /36b/ F.K. Lotgering, J. Phys. Chem. Sol. 35, 1633 (1974) /37/ A.M. van Diepen, F.K. Lotgering, i b i d 3 5 , 1641 (1974) /38/

F.K. Lotgering,

/39/ /40/ /41/

C. Sauer, N. Koebler, W. Zinn, i b i d 3 9 , 1197 (1978) G. Albanese, G. Asti, P. Batti, Nuovo Cimento 54B, 339 G. Albanese, G. Asti, P. Batti, Nuovo Cimento ~8B, 467

P.R. Lecher, R.P. van Stapele, ibid 4_~i, 481 (1980)

/42/ /43/

G. Albanese, M. Carbuoioohio, G. Albanese, M. Carbueicohio,

/44/

R.K. Gubajdullin, N.G. Ivojlov, E.S. Romanov, Sol. St. Physics 22, 267 (1980) G. Albanese, M. Carbuciochio, L. Pareti, S. Rinaldi, E. Lueehini, G. Slokar, J. Mag. Mag. Mat. 1~-18, 1453 (1980) H.W. Zandbergen, F.C. Mijlhoff, D.J.W. Ijdo, G. van Tendeloo, Mat. Res. Bull. 19, 1443 (1984)

(1968) (1968)

A. Deriu, Nuovo Cimento I~B, 147 (1973) A. Deriu, phys. stat. sol. (a) 23, 351

(1974)

/45/ /46/ /47/

E. Pollert, M. Nev~iva, L. Mat~jkov~,

J. Nov~k, Mat. Res. Bull. 16,

1499 (1981) /48/ /49/ /50/

/51/ /52/

/53/ /54/

G. Albeuaese, G. Albanese, G. Albanese,

O. Asti, P. Batti, Nuovo Cimento 58B, 480 (1968) M. Carbueicehio, A. Deriu, Nuovo Cimento I~B, 147 (1973) M. Carbuoicohio, F. Bolzoni, Physics B+C, 86-88, 941

(1977) A.H. Mones, E. Banks, J. Phys. Chem. Sol. ~, 217 (1958) M.A. Vinnik, R.J. Zvereva, Kristalografiya 14, 697 (1969) G. Albanese, A. Deriu, E. Lucchini, G. Slokar, IEEE Trans. Mag. 17, 2639 /1981) G. Albanese,

7_..~3, K193

M. Carbuoioohio,

(1982)

L. Pareti,

S. Rinaldi, phys. stat. sol.

Cw~alchemi~w of magneticoxides

203

/55/

V.l. Ivanova,

/56/ /57/

(1976) T.M. Perekalina, V.P. Cheparin, Sol. St. Phys. 9, 3205 (1967) O.P. Aleshko-Ozhevskii, R.A. Sizov, V.P. Cheparin, I.I. Yamzin,

/58/

P h y s . JETP 2 , 207 (1968) O.P. Aleshko-Ozhevskii, V.A. Ljubimov,

/59/ /60/

V.I. Gavrilova~

I.G. Fedorova, Neorg. materlaly 12, 712

Soy.

I.I. Yamzin, Kristalograflya

16, 823 (1971) 0 . P . A l e s h k o - O z h e v s k i i , V.A. L j u b i m t s e v , M . I . N a m t a l i s h v i X i , I . I . Yamzin, Kristalografiya 16, 711 (1972) 0.P. Aleshko-0zhevskii, I.I. Yamzin, V.P. Cheparin, P. Cherkasov, Kri-

/62/

stalografiya 18, 626 (1973) 0.P. Aleshko-0zhevskii, I.l. Yamzin, Krlstalografiya 13, 2543 (1971) M.I. Namtalishvili, O.P. Aleshko-Ozhevskii~ I.I. Yamzin, Sol. St. Phys.

/63/ /64/ /65/ /66/

13, 2543 (1971) H.A. Vinnik, R.I. Zvereva, Krlstalografiya 15, 964 (1970) R.A. Sizov, K.N. ZaJeev, Soy. Phys. JETP 66, 368 (1974) 0. Sohnltz-DuMont, H. Kasper, Z. Anorg. Allgem. Chem. ~41, 252 (1965) E.F. Bertaut, A. Desehamps, R. Pauthenet, S. Piokart, J . Phys. Radium

/61/

20, 404 (1959) /67/ /68/ /69/

P.M. Rao, A. Garard, F. GrandJean, J. Hag. Hag. Mat. I~-18, 645 (1980) P.M. Rao, A. G6rard, F. Grandjean, phys. stat. Sol. (a) 54, 529 (1979) X. Obradors, A. Isalgu6, A. Collomb, M. Pernet, J. Pannetier, J. Rodriguez, J. TeJada, J.C. Joubert,

IEEE Trans.

on Mag., Mag-20,

1636

(1984) /70/ /71/

X. 0 b r a d o r s , A. C o l l o m b , M. P e r n e t , Hag. Hat. 44, 118 (1984) X. O b r a d o r s , J . T e J a d a , A. I s a l g u 6 ,

/72/

E. Poilert,

821

/73/ /74/

/75/ /76/ /77/ /78/ /79/ /80/ /81/ /82/ /83/ /84/

d.C. Joubert,

A. I s a l g u 6 ,

J.C.

Sol. St.

Joubert,

J.

Mag.

Commum. 50,

(1984)

S. Krupi~ka, E. Kuzmi~ov~, J. Phys. Chem. Sol. 43~ 1137 (1982) J . A . M a m a l u j , L . P . , 0 1 o h o v i k , F i z . Teo~m. r y e . Day1. 17, 25 (1984) A. Tauber, J.A. Kohn, R.0. Savage, J. Appl. Phys. 34, 1265 (1963) M.C. Cad6e, D.J.W. Ijdo, J. Sol. St. Chem. 36, 314 (1981) F. Haberey, M. Velioesou, Aota Cryst. B~O, 1507 (1974) E. Kneller, M. Velioeseu, F. Haberey, J. Hag. Mag. Mat. ~, 49 (1981) X. 0bradors, A. CÙllomb, J. Pannetier, A. Isalgu6, J. Tejada, J.C. Joubert, Mat. Res. Bull. 18, 1543 (1983) F.K. Lotgering, U. Enz, J. Smit, Philips Res. Rept. 16, 441 (1961) J.P. Mahoney, A. Tauber, R.0. Savage, AIP Conf. Proo. ~, 816 (1972) J.P. Mahoney, A. Tauber, R.O. Savage, Aim Conf. Proo. i0, 159 (1972) F.K. Lotgering, J. Phys. Chem. Sol. 35, 1633 (1974) A. Desehamps, Z. Angew. Phys. 26, 190 (1969) A.D. Suohurova, T.M. Perekalina, V.P. Cheparin, Zh. Eksp. Teor. Fiz. 55, 1166 (1968)

E. Pollert

204

/85/

V.F. Belov, T.A. Khimieh, M.N. Shipko, I.S. Zheludev, E.V. Komneev, N.

/86/

E. Kreber, U. Gonser, Appl. Phys. i0, 175

/87/

E. Pollert, will be published

/88/

M. Krupka, private eommunieation, will be published

/89/

H. Kojima, K. Haneda, Prec. Int. Conf. Ferrites Kyoto 1970, 380

/90/ /91/

B. Durand, J.M. Paris, Ann. Chim. Fr. ~, 589 (1980) Y. Gore, M. Higashimoto, K. Takahashi, Jap. J. Appl. Phys. 12, 945

/92/

H. NeumSxm, H.P.J. WiJn, J. Am. Cer. See. 51, 536

/93/

F.K. Lotgering, P.H.G.M.

/94/ /95/

P.E.D. Morgan, T.M. Shaw, Mat. Res. Bull. 18, 539 (1983) N. Iyi, S. Takekawa, Y. Bando, S. Kimura, J. Sol. St. Chem. ~7, 34

/96/

(1983) N. Iyi, Z. Inoue,

/97/

(1984) F.P.F. van Berkel, H.W. Zandbergen, O.C. Versohoor, D.J.W. ljdo, Aeta

S. 0vanesyan,

Zh. Eksp. Teor. Fiz. 64, 2160 (1973) (1976)

(1973)

Cryst. C40, 1124 /98/ /99/

(1968)

Vrom~ns, J. Am. Cer. See. 60, 416 (1977)

S. Takehawa, S. Kimura, J. Sol. St. Chem. 52, 66

(1984)

T. Wagner, M.0"Keefee, Aota Cryst. B41, 108 (1985) H.W. Zandber~en, F.C. Mijlhoff, D.J.W. Ijdo, G. van Tendeloo, Mat. Res Bull.

_19,

1443

(1984)

Crystal chemistry of magnetic oxides

205

THE AUTHOR

E. POLLERT

Emil Pollert

graduated

in 1961 at the I n s t i t u t e

P r a g U e w h e r e he later r e c e i v e d also his PhD w o r k in 1962 i n the I n s t i t u t e te)~ A c a d e m y laboratory

of Sciences,

of m a ~ n e t i o

of S o l i d S t a t e P h y s i c s

Pra6-ue a n d since

oxides

technology.

The orientation

of the

of his w o r k h a d

of S o l i d S t a t e C h e m i s t r y

in

i n 1 9 7 3 - 7 4 and f o l l o w i n ~ c o o p e r a t i o n w i t h this l a b o r a t o r y .

His m a i n r e s e a r c h a c t i v i t y and characterization phase equilibria his i n t e r e s t His

in

(now P h y s i c a l I n s t i t u -

1975 he is there a leader

b e e n i n f l u e n c e d by his stay i n the L a b o r a t o r y Bordeaux

of C h e m i c a l T e c h n o l o g y

. He s t a r t e d w i t h the r e s e a r c h

includes problems

of m a g n e t i c

c o n n e c t e d w i t h the p r e p a r a t i o n

oxide m a t e r i a l s

and 6 T o w i n ~ of single

crystals.

also to the p h o t o e l e o t r o o h e m i o a l

leisure-time

activity

is d e v o t e d

c a n o e i n g and d o w n h i l l skiing.

to sport,

like c r y s t a l c h e m i s t r y , I n the last y e a r s he t u r n e d

properties

of these m a t e r i a l s .

particularly white-water