Raman spectra of binary tellurite glasses containing tri- or tetra-valent cations

Raman spectra of binary tellurite glasses containing tri- or tetra-valent cations

JOURNAL OF NON IIINNION ELSEVIER Journal of Non-CrystallineSolids 19i (1995) 115-123 Raman spectra of binary tellurite glasses containing tri- or t...

625KB Sizes 3 Downloads 24 Views

JOURNAL OF

NON IIINNION ELSEVIER

Journal of Non-CrystallineSolids 19i (1995) 115-123

Raman spectra of binary tellurite glasses containing tri- or tetra-valent cations Takao Sekiya *, Norio Mochida, Ayako Soejima Faculty of Engineering, YokohamaNational University 156, Tokiwadai, Hodogaya, Yokohama240, Japan

Received26 July 1994;revised manuscriptreceived2I April 1995

Abstract Glass formation and structure are investigated in binary tellurite systems containing YO3/2, InO3/2, LaO3/2, ZrO2, SnO2, HfO2, and ThO 2 as second components. No glasses are obtained in two systems, ZrO2-TeO2 and SnO2-TeO 2, because of the precipitation of ZrTe308 and SnTe30 8 crystals. Raman spectra and glass properties, such as transition temperature, thermal expansion and density, were measured. Glasses having low LaO3/2 content have a continuous network structure composed of corner-sharing TeO4 trigonal bipyramids and TeO3+ 1 polyhedra having one non-bridging oxygen atom. Further increase of LaO3/2 content accelerates a conversion of TeO4 trigonal bipyramids and TeO3+ i polyhedra into TeO3 trigonal pyramids having two or three non-bridging oxygen atoms. In the YO3/2-TeO 2 and ThO2-TeOz systems, the change of glass structure follows the same process as in LaO3/2-TeQ glasses. In 23INO3/2 . 77TeO2 glass, few structural fragments composed of TeO 3 trigonal pyramids are formed. There is a possibility that 5HfOz . 95TeOz glass contains a small fraction of structural fragments present in HfTe308 crystal.

1. Introduction At present, there is an increasing interest in studying tellurite glasses which have high refractive index, good infrared (IR) transmittance and optical non-linearity [1-8]. Since oxides of the elements in groups ErI and IV are classified into three categories, glassformers, intermediates and modifiers [9-11], a systematic investigation of the structure of tellurite glasses containing such oxides as a second component is of great interest. The authors previously investigated tellurite glasses containing glassformers, such as B20 3, SiO 2, GeO z and As20 3 [12-14]. In this study, the authors investigate binary

* Correspondingauthor. Tel: +81-45 335 1451.Telefax: +8145 331 6143.

tellurite glasses containing tri- or tetra-valent modifiers, Y203, In203, La203, ZrO 2, SnO 2, HfO 2, and ThO 2, as second components. So far, many studies have been conducted on the thermal, elastic and optical properties of binary tellurite glasses containing rare-earth oxides [15-17]. However, there are few reports on the structure of the glasses containing such oxides. Qiu et al. [18] investigated the constitution of InzO3-TeO 2 glasses by Raman and infrared spectroscopy and detected the formation of TeO 3 trigonal pyramids (tps). The aim of this study is to reveal the change in coordination state of tellurium atoms depending on composition on the basis of the compositional dependence of Raman spectra of such tellurite glasses. In order to provide data on the properties of these tellurite glasses, the transition temperature, thermal expansion and density were measured.

0022-3093/95/$09.50 © 1995 ElsevierScienceB.V. All rights reserved SSDI 0022-3093(95)00290- I

7". Sekiya et al./ Journal of Non-Crystalline Solids 191 (1995) 115-123

116

2. Experimental procedure Reagent-grade TeO2, Y203, In203, La203, ZrO 2, SnO2, HfO 2 and Th(NO3)4.4HzO were used as starting materials. Batches of 5.0 g were melted in a platinum crucible of 20 mm diameter at 800-1000°C for 10-30 rain. During the melting, the crucible was covered with a platinum lid to minimize vaporization of the constituents. Glasses were obtained by dipping the crucible bottom into ice-cold water. TeO 2 glass was prepared in a way previously used [19]. The sample was judged to be in the vitreous state from its appearance and X-ray diffraction (XRD) with Cu Kc~ rays at room temperature. The glass composition was determined using predetermined ignition loss of second components. The samples were cooled at a rate of 2°C/rain from a temperature higher than the glass transition temperature and lower than the deformation temperature. The glass transition and thermal expansion were measured at a heating rate of 2°C/min with a vertical fused-silica dilatometer. All thermal expansion coefficients were determined over the range from 50 to 300°C. The density of the annealed glass was determined at room temperature by the Archimedes displacement method with xylene as the immersion liquid. Some binary crystals were prepared and their Raman spectra were measured in order to make a comparison with those of the glasses. The InzTe309 crystal was prepared by heating stoichiometrically mixed powder of TeO 2 and In203 at 600°C for 4 days in a vacuum in a silica glass ampule. La2Te4Oi1 and Pr2Te4Oli crystals were pre-

pared by firing a weighed mixture of the rare-earth oxide and TeO 2 at 600 and 700°C for 18 and 24 h, respectively. SnTe3Os, ZrT%O a and HfT%O a crystals were obtained by heating TeO 2 with the corresponding oxides at 650-700°C for 6-18 h. All the crystalline phases were identified by XRD. Raman spectra were recorded in the wave number range from 50 to 1200 cm -1 with a R-800 laser Raman spectrophotometer (Jasco) equipped with a triple-monochromator. The digital intensity data was recorded at intervals of 1 cm -I. The specimen was excited with an argon ion laser (Lexel) of 1.4 mm diameter at 514.5 nm with a power of about 200 roW. The spectrum was observed at an angle of 90 ° to the exiting light. The intensities of the Raman spectra of glass specimens having different compositions were normalized with respect to the glass composition by the internal standardization technique with a standard compound of 40T1Ot/2.60SiO z (mol%) glass [13,20-23] and the Raman spectrum was deconvoluted into symmetric Gaussian-type functions [13,20-23].

3. Results Table 1 shows the products that the authors obtained. Except for the LaO3/2-TeO 2 system, the glass formation range of the binary glasses is equal to that determined by Imaoka and Yamazaki [24]. No glasses were obtained in the SnO2-TeO z and ZrO 2TeO z systems.

Table 1 Vitrified composition and precipitated phases on cooling the melt Second component Content (mol%)

YO3/2 InO3/2 LaO3/2 ZrO2 SnO2 ThO2 HfO 2

5

10

I5

20

25

O O O

0 0 0

Y2Te6015 © ©

O ©

In2Te309 ©

O Hf'fe308 +TeO2

ThTe206

( ZrTe3Q +TeO2 (SnTe308 +TeQ O 0

O, clear glass was obtained.

30

( La2T%O~s +La2Te4Ott

T. Sekiya et al./Journal of Non-Crystalline Solids 191 (1995) 115-123

117

Fig. 1 shows intensity-normalized Raman spectra of the binary tellurite glasses• Fig. 2 shows results of band deconvolution of the spectra of TeO 2, 23INO3/2 • 77TeO 2, 25LAO3/2 . 75TeO 2 and 5HfO 2 • 95TeO z glasses. Agreement between the observed and simulated spectra is quantitatively evaluated by R defined as

(a)

R = E t lobs(v) -- Icaic( v ) l / ~ [

lobs( V)l, p

" i .x= 0

_

x= 5 x=lO

x--!5 x-- o 1200 1000 800 600 400 Wavenurnber (cm"~)

200

where the summation was carried out over the number of the intensity data. The average and maximal values of R were 0.02 and 0.03, respectively. A good agreement was obtained between the observed and simulated spectra. The spectral deconvolution of the binary glasses indicates that five bands are present at about 780, 730, 660, 610 and 450 cm -~ in the wave number range over 400 cm -1 and that 5HfO 2 • 95TeO 2 glass has a sixth band at about 860 cm -1. The five bands are named A, B , C, D and E, respectively. The frequency shifts of the peaks of the five bands are -- 20 cm -~. Fig. 3 shows the compositional dependence of the intensities of the deconvoluted bands of the binary glasses. The ordinate shows the reduced intensities when the intensity of band C

(b) (c)

T ¢-

\ 1200 1000

800

600

400

200

Wavenumber (cm-~) Fig. 1. Intensity-normalized Raman spectra: (a) xLaO3/2 -(100x)TeO2 glasses, (b) xInO3/2-(100- x)TeO z glasses, (c) TeO2, 10YO3/2 •90TeO2, 10ThQ •90TeO2 and 5HfO2 . 95TeOz glasses.

5Ht:02.95T/ 1200

1000

800 600 400 Wavenumber (cw ~) Ng.l(continued).

200

T. Sekiya et aI./ Journal of Non-Ctystalline Solids 191 (1995) 115-123

118

(b) 2.0 |

TeO~

if\

1'6{~ °

1.6

.~, 1.4

I \E - 1'2 r \

'.°h4. o\ 0.6

5F20~a'9~

l

0.4~,~,~,~ ,~

O,4tc

0 . 2 ~ ~ _

0,2

0 0 10 20 30 LaO~2Content (tool%)

00 1'0 YOa~zContent (mo[%)

(c) 2.0 1.8

"\

(d) 2.0,

1,8

q

1.6

1.6

1000 800 GO0 400 Wavenumber (cm"~ )

200

Fig. 2. Deconvolution of Raman spectra of TeO 2 23INO3/2" 77TeO2 25LaO3/2 ' 75TeQ and 5HfO 2. 95TeO 2 glasses using a symmetric Gaussian-type function.

,,<.4

,~1.4

qE

z 1.2

a, 1.2

1.0i

1,0

u

rv

of TeO 2 glass is taken to be 1.00. The bands A - E are mainly attributed to the vibrations of coordination polyhedra of tellurium atoms. In order to eliminate the influence of the glass composition, the reduced intensities of the bands were calculated by dividing areas of deconvoluted bands by the TeO 2 content. The Raman spectra of In2Te309, La2Te40]], Pr2Te4Oi1, S n T % Q ZrTe30 a and H f r % o 8 crystals are shown in Fig. 4. The compositional dependences of the molar volume, Vm, glass transition temperature, Tg, and thermal expansion coefficient, o~, are shown in Figs. 5, 6 and 7, respectively. The Vm, Tg and o~ of the glasses change linearly with composition. There are a few reports on the properties of LaO3/2-TeQ glasses

Fig. 3. Compositional dependence of the intensities of the deconvoluted bands observed in the Raman spectra of the glasses: (a) LaO3/2 -TeO 2, (b) YO3/2 -TeO 2, (c) InO3/2 -TeO 2, (d) ThO 2 T e Q , (e) HfO 2 -TeO 2. The lines are drawn as guides for the eye.

\

t~

0.6

0,6

0.4~(

0.4;i

0.2

0.2

0 0 10 20 30 InO:~ Content (moP/,) (e)

~o-B

0 0 I'0 Th02 Content (mot'/,)

2,0 -OE 1.8 1.6

.•1,4

1,2

~.o!

\v C

0,2

0 0 1'0 H(O= Content (tool%)

T. Sekiya et al. / Journal of Non-Crystalline Solids 191 (1995) 115-123

119

18.0 I~T~

~18.0

M=~T~h~M=Y M=In 14.0 1'0 2'0 30 MO. Content (mol°/o)

i-., N

La2Te40,

P~Te40.

~c.o

~

09 C ID -4J

eA

t-

SnTea08

~

~

A

1200 l obo

~

860

66o

Wavenumber

460

260

29.0 / o " M=Th

E

28.5 , , , ~ M: La

28.0

o \ M=Y

E

27.5

M=In ck

I'0 2'0 3'0 NO Content (moP/,) Fig. 5. Compositional dependence of the molar volume, Vm, of MO,,-TeO 2 glasses. The lines are drawn as guides for the eye.

400F

[15,16]. The Vm of 28.2 cm3/mol for 18.2LAO3/2 . 81.8TEO 2 glass (30.999 cm3/mol for (La203)0. I . (TeO2)0. 9 glass) [16] is consistent with our result, but the other data are inconsistent with ours.

4. Discussion

(cm "~ )

Fig. 4. Raman spectra of InzTe309, La2Te4Oll, Pr2Te4Oll, SnT%O s, ZrT%O s and HfTe30 ~ crystals.

2

Fig. 7. Compositional dependence of the thermal expansion coefficient, ~, of MO,-TeO 2 glasses. The lines are drawn as guides for the eye:

L

~

Zr'Te3&

~ = L a

M=La

L=th 3000 10 20 30 MOyContent (mot'/,) Fig. 6. Compositional dependence of the glass transition temperature, T~, of MO,,-TeO 2 glasses. The lines are drawn as guides for the eye.

4.1. LaO3/2-TeO 2 and YO.~/2-TeO 2 glasses The structural change in LaO3/2-TeO 2 gtasses resembles that of alkali and alkaline-earth tetlurite glasses [20,21]. The Raman spectra and compositional dependence of the deconvoluted bands of LaO3/a-TeO2 glasses show that an increase in LaO3/2 content results in a decrease in intensity of the bands C (660 cm-1), D (610 cm -1) and E (450 cm - 1), and an increase of bands A (780 cm - 1) and B (730 cm-1). The intensity of the band B (730 cm -1) has a maximum at about 15 mot%. When the LaO3/2 content exceeds t5 mol%, a new broad band is observed at about 330 cm -t. These changes in the spectra are similar to those observed in alkali and alkaline-earth tellurite glasses. The deconvoluted bands A - E are assigned in conformity with our previous works concerning TeO 2 and alkali tellurite glasses [19,20], as follows. The intensity of band A is due to both a vibration of a continuous network composed of TeO4 trigonal bipyramids (tbps) and a stretching vibration of tellurium and non-bridging oxygen (NBO) atoms in TeO3+ 1 polyhedron or TeO 3 tp. Band B consists not only of a vibration of the continuous network composed of TeO 4 tbps but also of a stretching vibration between tellurium and NBO atoms. The NBO atoms

T, Sekiya et al. / Journal of Non-Crystalline Solid7 191 (1995) 115-123

I20

are formed in T e O 3 + 1 polyhedron or T e O 3 tp and interact weakly with adjacent tellurium atoms, where the symbol, NBO, represents the oxygen atoms forming Te--O and T e - O - , and their resonating bonds. In this case, the bond between NBO and tellurium atoms is weakened and, therefore, the vibration appears in the lower wave number region than band A. Band C is assigned to antisymmetric vibrations of Te-s,ortOiong--Te linkages, such as Tew-eqOax-Tetv, T e m + i - O . . . T e m + t , T e m - O " ' T e l i x + i , TeiveqO...Teiil+l, TeHi+i-Oax-Telv and T e i I i - O a x Telv linkages. Since the tellurium atom forming the Te-longO bonds, such as Teiv-ax O and Telli+ I . .. O bond, forms a TeO 4 tbp or TeO 3+I polyhedron, the intensity of band C is, in part, due to a fraction of the tellurium atoms forming TeO 4 tbps and TeO3+ 1 polyhedra. Band D is assigned to a vibration of the continuous network composed of TeO4 tbps. Band E is assigned to symmetric stretching (and bending) vibrations of T e - O - T e linkages which are formed by sharing vertices of tellurium-oxygen coordination polyhedra. Therefore, the occurrence of band E indicates the presence of a continuous network consisting of tellurium-oxygen polyhedra. The authors assign the new band at 330 c m -1 to a bending vibration of TeO 3 tp having two or three NBO atoms. The same vibrations are observed at about 270 cm-1 in alkali tellurite glasses [20]. It is assumed that a difference in coordination to NBO atoms between lanthanum and alkali ions makes a contribution to the shift of the bending vibration from 270 to 330 cm

-!

We discuss the reasonableness of the above-mentioned assignments of the bands on the basis of relation between the structure and Raman spectra of La2Te4Oll and Pr2Te4Oll crystals. La2Te4011 and Pr2Te4Oi 1 crystals are isomorphous with Nd2Te4Oll crystal [25,26]. Castro et al. [27] reported that, in Nd2Te4Oll crystal, two different tellurium atoms are in 3 + 1 coordination. When the bond valence model [28-30] is applied to interpret the coordination state of the tellurium atoms, the formula S = 1.333 (r/0.1854) -5'2 [29] gives the valence value of 0.19 for T e ( 1 ) . . . 0(4) bond, where r and S are the Te-O distance and valence, respectively, and numbering of atoms is from Ref. [27]. This value is very small compared with the shorter three bonds, as shown in Table 2. Therefore, the T e ( 1 ) . . . 0(4)

Table 2 Interatomic distance and valence of Te-O pairs in NdzTe4OIi crystal Distance (nm)

Bond valence u

Te(i)-O(3) 0(2) O(1) 0(4)

0.I 863 0.1877 0.i883 0.2694

1.30 1.25 1.23 0.19

Te(2)-O(5) 0(4) 0(6) 0(1)

0.1830 o, 1876 0.1989 0,2434

1.42 1,25 0.93 0.32

a Bond valence is calculated using S = 1.333 (r/0,1854) -'~'2 [I5],

bonds can be neglected, although weak interactions may exist. In this case, Te(1) and Te(2) form TeO 3 tp with two NBO atoms and TeO3+ l polyhedron with two NBO atoms, respectively. Two Te(2)O3+ 1 polyhedra are connected by sharing 0(6) and each Te(1)O 3 tp shares O(1) with a Te(2)O3÷l polyhedron, tlaereby forming a Te(1)2Te(2)zOil 6- ion. In Raman spectra of La2Te4Oll and Pr2Te4Oll crystals, the band at about 790 cm-1 is assigned to a stretching vibration between tellurium and NBO atoms. The presence of the bands at about 700 and 650 cmshows NBO atoms interacting weakly with adjacent tellurium atoms and Tem+i . . . O-Te m linkages, respectively. The existence of TeO 3 tp with two or three NBO atoms results in the appearance of the band at about 300 cm -~. The bands at about 400 cm -1 can be assigned to symmetric stretching (and bending) vibration of Te-O-Te linkage. There is a small difference in band frequencies between actual observation in La2Te40~ crystal and our expectation. On the basis of the assignments of the bands, we discuss the structure of LaO3/2-Te Q glasses. The decrease in intensity of band E and the increase of bands A and B indicate a cleavage of Te-O=Te linkage and a formation of NBO atoms [20]. This structural change results in a conversion of TeO 4 tbps to TeO3+ ~ polyhedra having one NBO atom. Since NBO atoms interacting weakly with adjacent tellurium atoms are increased in numbers with the increase in intensity of band B, those telluriumoxygen polyhedra form a continuous network. These indicate that glasses having low LaO3/z content have a continuous network structure composed of cornet'-

12i

Z Sekiya et al./Journal of Non-Crystalline Solids 191 (1995) 115-123

sharing TeO4 tbps and TeO3+ I polyhedra having one NBO atom. The decrease in intensity of band C and the appearance of the new broad band at about 330 cm -~ indicate that an increase in LaO3/2 content over 15 mol% accelerates a conversion of TeO 4 tbps and TeO3+ 1 polyhedra into TeO 3 tps having two or three NBO atoms. In glasses containing more than 15 mol% LaO3/2, the downward tendency in intensity of band B indicates a formation of small structural fragments composed of TeO 3 tps having two or three NBO atoms. It is uncertain why the intensity of band B increases again with an increase in LaOv2 content. We think that structural units constituting La2Te6015 crystal may contribute to the intensity of band B. The 25LaOv2 • 75TeO 2 glass has the same composition as metastable La2Te6015 crystal which has the fluorite-type structure with incomplete population of the anion position [31] and is primarily precipitated on heating the glass at 427°C. Tr~Smel et al. [31] suggest that, in the La2Te60~5 crystal, the tellurium atom has a different coordination state from ones previously assumed [29,32-34]. The Raman spectrum of the La2T%OI5 crystal is omitted because the crystatlite could not be separated from the amorphous phase. Because of the glass-formation range, we will not discuss the structure of YO3/2-TeO 2 glasses. However, we assume that the structure of YO3/2-TeO 2 glasses resembles that of LaO3/2-TeO 2 glasses having corresponding composition because of a resemblance between their Raman spectra (Fig. 1), of a similarity in the compositional dependence of the Raman band intensities (Fig. 3) and of a similarity in chemical properties of y3+ to La3+ [35,36]. 4.2. InO3/2-Te02 glasses

We discuss a coiTelation between the structure and Raman spectrum of the InaTe30 9 crystal. If the assignments carried out in the previous section are used for interpretation of the spectrum of the In2T%O 9 crystal, the existence of bands at about 435 and 600-650 cm-~ indicates that the presence of T e - O - T e and Te-~hortOlong-Te linkages, respectively. However, Philippot et al. reported that, in the In2T%O 9 crystal, all the tellurium atoms form TeO 3 tps having three NBO atoms [37]. In order to resolve

Table 3 Interatomic distance and valence of Te-O pairs in In2T%O9 crystal Distance(nm) Bond valence Te(1)-O(5) 0(4)×2 0(5') 0(4') × 2

0.i889 0.1899 0.2694 0.2727

1.2I 1.18 0. I9 0.18

Te(2)-O(l) 0(3) 0(2) O(4) 0(5) O(1)

0.1887 0.1935 0.I943 0.2482 0.2541 0.2734

122 1.07 1.04 O.29 0.26 0. I8

a Bondvalenceis calculatedusing S = 1.333(r/0.1854)-52 [15].

this contradiction, we re-examine the coordination state of tellurium atoms in the In;T%O 9 crystal on the basis of the bond valence model [28-30]. Table 3 shows Te-O distance and estimated bond valence using the formula S = 1.333(r/0.1854) -5'2 [29]. The valence values of Te(2) .. • 0(4) and Te(2) .. • 0(5) pairs are small but are not negligible. The authors conclude that the coordination state of Te(2) should be regarded as 3 + 2. Consequently, in In2T%O 9 crystal, Te(1) connects two Te(2) forming Te(1)0 ( 4 ) . . . Te(2) linkages and shares 0(5) with two other Te(2), yielding infinite chains. In the Raman spectrum of the In2Te30 9 crystal, the bands at about 700 cm -I which can be assigned to a stretching vibration between tellurium and NBO atoms, appear in a lower wave number region than expected. Each Te(2) has three NBO atoms and the Te(2)-O- bonds are slightly longer than those in other crystals. The electrostatic influence of T e ( 2 ) . . . 0(4) and T e ( 2 ) . . . 0(5) bonds will weaken the Te(2)-Obonds. The band at about 320 cm-I will arise from Te(2) having plural NBO atoms. This assignment indicates that the band assignments made in the previous section can be employed to interpret the deconvoluted bands of InOv2-TeO 2 glasses and that bands A - E of InOv2-TeO 2 glasses arise mainly from tellurium-oxygen polyhedra. An increase in intensity of bands A and B with increasing InO3/2 content indicates the formation of NBO atoms. The formation of NBO atom in TeO 4 tbp distort into TeO3+ 1 polyhedron having one NBO

122

T. Sekiya et al. / Journal of Non-Crystalline Solids 191 (1995) 115-123

atom. As the InO3/2 content increases, the intensities of bands C and E decrease. These are caused by a conversion of TeO 4 and TeO3+ l polyhedra into TeO 3 tps and a cleavage of Te-O-Te linkages, respectively. The slopes of the intensities of bands C and E are, unexpectedly, small compared with those in LaO3/2-TeO 2 glasses. Under an ideal condition, the mole fractions of MO3/2 at which all the tellurium atoms form TeO 3 tps and no Te-O-Te linkages, are estimated to be 25 and 40 mol%, respectively. We conclude, therefore, that the influence of indium oxide on breaking tellurium-oxygen networks is smaller than that of lanthanum oxide. In 23INO3/2 • 77TeO 2 glass, an absence of bands assigned to bending vibrations of TeO 3 tp having two or three NBO atoms indicates that there exist few isolated structural fragments composed of such TeO 3 tps. These form a contrast with 25LaO3/2 • 75TeO 2 glass.

these systems. SnTeaO 8 ZrTe308 and HfTe30 s crystals are isomorphous with TiTe308 crystal [39]. MTeBO 8 (M--Ti, Zr, Sn and Hf) crystals are composed of MO 6 octahedra and TeO 4 tbps. The MO 6 octahedron shares a common oxygen atom with TeO 4 tbp forming Te-eqO-M linkage and three TeO 4 tbps are connected by sharing axial vertices yielding three-coordinated oxygen atom. The lack of flexibility of the three-coordinated oxygen atom will lead to crystallization [40]. Tile structure of 5HfO 2 . 95TeO 2 glass is somewhat different fl'om that of ThOz-TeO a glasses. The sixth band observed at about 860 cmin the Raman spectrum of the glass is comparable with the band at about 850 cm-I in the spectra of MTe30 a crystals. There is a possibility that the glass contains a small fraction of structural fragments present in MTe30 a crystals.

4.3. Binary tel&rite systems containing tetra-valent cation

5. Conclusion

The structural change in ThO2-TeO 2 glasses resembles that in LaO3/2-TeO 2 glasses. As the ThO 2 content increases, bands C, D and E decrease in intensity and the intensities of bands A and B increase. The assignments of bands A - E in LaO3/2TeO 2 glasses are applicable to an interpretation of the structure of ThO2-TeO 2 glasses, because both lanthanum and thorium oxides are network modifiers [9-11]. The compositional dependence and assignments of the bands indicate that an addition of ThO 2 induces a cleavage of T e - O - T e linkages, a formation of NBO atoms and a conversion of TeO 4 tbps into TeO3+ I polyhedra. It is ambiguous whether TeO 3 tps having two or three NBO atoms are present in the glasses, because of an absence of the bending vibration in the spectra. We nevertheless think that such TeO 3 tps may exist because of the decrease in intensity of band C and of the precipitation of ThTe206 crystal composed of TeO 2- ions [38] from the melt of 15ThO 2 • 85TeO 2. SnO2-TeO 2 and ZrO2-TeO 2 systems have no vitrified ranges and the HfO2-TeO 2 system has a narrow glass-formation range. Table 1 clearly shows that the precipitation of SnTe308, ZrTe308 and Ht'Te308 crystals interferes with glass-formation in

With an increase in LaO3/2 content, the coordination state of the tellurium atom changes fl'om TeO 4 tbp through TeO3+ t polyhedra to TeO 3 tp and NBO atoms increase in number. Glasses having low LaO3/2 content have a continuous network structure composed mainly of TeO 4 tbps and TeO a + ~ polyhedra having one NBO atom, while glasses containing more than 15 mol% LaOv2 contain small structural fragments composed of TeO 3 tps having two or three NBO atoms. YO3/a-TeO 2 glasses have the same structural change depending on composition as LaO3/z-TeO 2 glasses. An addition of InO3/2 results in a reduction of Te-O-Te linkages and formation of NBO atoms. 23InOv2.77TeO 2 glass contains few structural fragments composed of TeO 3 tps. The influence of indium oxide on breaking telluriumoxygen networks is less than that of lanthanum oxide. In ThO2-TeO 2 glasses, a formation of NBO atoms and a conversion of TeO4 tbps into TeO3+ ~ polyhedra are also detected. The precipitation of MTe30 s (M = Sn, Zr and Hf) crystals prevents the melts in binary tellurite systems from being in a homogeneous vitreous state. Properties of the binary glasses, such as transition temperature, thermal expansion and molar volume, are linearly dependent on composition.

7". Sekiya et aI. / Journal of Non-Crystalline Solids 191 (1995) 115-123

References [I] J.E. Stanworth, J. Soc. Glass Technol. 36 (1952) 217T. [2] J.A. James and J.E. Stanworth, J. Soc. Glass Technol. 38 (1954) 421T. [3] J.E. Stanworth, J. Soc. Glass Technol. 38 (1954) 425T. [4] N.F. Bon'elli, J. Chem. Phys. 41 (1964) 3289. [5] A.K. Yakhkind, J. Am. Ceram. Soc. 49 (1966) 670. [6] M.J. Weber, D. Milam and W.L. Smith, Opt. Eng. 17 (1978) 463. [7] E.M. Vogel, M.J. Weber and D.M. Krol, Phys. Chem. Glasses 32 (199I) 23I. [8] H. Nasu, O. Matsushita, K. Kamiya, H. Kobayashi and K. Kubodera, J. Non-Cryst. Solids 124 (i990) 275. [9] K.H. Sun, J. Am. Ceram. Soc. 54 (1932) 3841. [10] A. Dietzel, Naturwiss. 29 (1941) 537. [l l] J.E. Stanworth, J. Soc. Glass TechnoI. 30 (1946) 56. [12] N. Mochida and T. Sekiya, Nippon Sheet Glass Foundation Mater. Science Rep. 6 (1988) 180. [I3] T. Sekiya, N. Mochida, A. Ohtsuka and A. Soejima, J. Non-Cryst. Solids 151 (1992) 222. [14] T. Sekiya, N. Mochida, A. Ohtsuka, A. Soejima, A. Yasumori and M. Yamane, Glastech. Bet. 66 (1993) 15. [15] S.H. Kim, T. Yoko and S. Sakka, J. Am. Ceram. Soc. 76 (i993) 865. [16] R. E1-Mallawany, J. Mater. Res. 7 (1992) 224. [17] R.A. E1-Mallawany and G.A. Saunders, J. Mater. Sci. Lett. 7 (1988) 870. [18] J.R. Qiu, A. Osaka, T. Namba, J. Takada and Y. Miura, J. Mater. Sci. 27 (1992) 3793. [19] T. Sekiya, N. Mochida, A. Ohtsuka and M. Tonokawa, J. Ceram. Soc. Jpn. 97 (1989) 1435. [20] T. Sekiya, N. Mochida, A. Ohtsuka and M. Tonokawa, J. Non-Cryst. Solids 144 (I992) 128.

123

[21] T. Sekiya, N. Mochida and A. Ohtsuka, J. Non-Cryst. Solids 168 (1994) 106. [22] T. Sekiya, N. Mochida and S. Ogawa, J. Non-Cryst. Solids 176 (1994) 105. [23] T. Sekiya, N. Mochida and S. Ogawa, J. Non-Cryst. Solids 185 (1995) 135. [24] M. Imaoka and T. Yamazaki, J. Ceram. Assoc. Jpn. 76 (I968) 160. [25] M.J. Redman, W.P. Binnie and J.R. Carter, J. Less-Comm. Met. 16 (1968) 407. [26] C. Parada, J.A. Alonso and I. Rasines, Inorg. Chim. Acta 1l i (1986) 197. [27] A. Castro, R. Enjalbert, D. Lloyd, I. Rasines and J. Galy, J. Solid State Chem. 85 (1990) 100. [28] I.D. Brown and K.K. Wu, Acta Crystallogr. B32 (I976) 1957. [29] E. Philippot, J. Solid State Chem. 38 (I98I) 26. [30] I.D. Brown and D. Altermatt, Acta Crystallogr. B41 (1985) 244. [31] M. Tr~Jmel, W.J. Hiitzler and E. MUnch, J. Less-Comm. Met. I lO (I985) 421. [32] I.D. Brown, J. Solid State Chem. I I (974) 214. [33] J. Galy, G. Meunier, S. Andersson and A. ,~strbm, J. Solid State Chem. 13 (1975) 142. [34] M. Tr~mel, J. Solid State Chem. 35 (1980) 90. [35] N.E. Topp, The Chemistry of the Rare Earth Elements (Elsevier, Amsterdam, 1965). [36] F.A. Cotton and G. Wilkinson, Basic Inorganic Chemistry (Wiley, New York, i976). [37] E. Philippot, R. Astier, W. Loeksmanto, M. Maurin and J. Moret, Rev. Chem. Miner. 15 (i978) 283. [38] M.L. Lopez, M.L. Veiga, A. Jerez and C. Pico, J. LessComm. Met. 175 (1991) 235. [39] G. Meunier and J. Galy, Acta Crystallogr. B27 (1971) 602. [40] M. Imaoka, J. Ceram. Assoc. Jpn. 67 (1959) 364.