Growth of Mo3Ir single crystals

Growth of Mo3Ir single crystals

Journal of Crystal Growth 72 (1985) 745—747 North-Holland, Amsterdam 745 LETFER TO THE EDITORS GROWTH OF Mo3Ir SINGLE CRYSTALS René KOKSBANG and Sve...

204KB Sizes 4 Downloads 92 Views

Journal of Crystal Growth 72 (1985) 745—747 North-Holland, Amsterdam

745

LETFER TO THE EDITORS GROWTH OF Mo3Ir SINGLE CRYSTALS René KOKSBANG and Svend Erik RASMUSSEN Department of Inorganic Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark Received 15 January 1985 3 were obtained. The crystals were examined by X-ray, Mo3y-ray Ir wasand prepared neutronbydiffraction, floating zone andmelting by measurement and singleof crystals criticaloftemperature up to 10 mm for superconductivity.

Mo 3 Jr has the A15, or $-W structure and is a superconductor with a reported critical temperature in the range 8.11—8.8 K [1,2]. In order to compare Mo3Ir with other A15 compounds, we decided to grow crystals of it large enough for neutron scattering measurements. As far as we know, no attempts to grow single crystals of this compound have been reported before. The phase diagram of Mo and Jr has been studied by Raub [3], Michalik and Brophy [4] and Giessen, Jaehnigen and Grant [5]. Their results are summarized in Constitution of Binary Alloys [6] and Handbook of Binary Phase Diagrams [7]. The phase diagram shows three stable intermetallic phases and a a-phase, Mo071 Jr029, which is only stable above 1975°C.Three of the phases, Jr3 Mo, Mo3Jr and the a-phase melt peritectically and one, MoIr, is formed by a solid state reaction [2]. The compound Mo3 Jr exists in a narrow cornposition range from 75% to 78% Mo and melts at 2110°Cwhere it is in equilibrium with a melt with the composition Mo070 Jr030. The a-phase is in equilibrium with a melt of composition Mo0691r031 and a solid solution of 63% Jr in Mo. Thus the two phases are in equilibrium with melts of nearly the same composition Both phases exist in equilibrium with the melt in very narrow temperature ranges only. In spite of these difficulties it is possible to grow single crystals using a floating zone method [8]. The materials used were Mo (Koch-Light Lab., .

99.95%) and Jr (Degussa) both as powders. The mixed powder was pressed in a sealed and evacuated rubber mould at an isostatic pressure of 2 MPa. Rods of 6 mm diameter and 100—120 mm length were then sintered in the usual way at temperatures up to 1900°C. The experimental setup for the floating zone experiment is shown in fig. 1. Crystal growth was achieved under a high pressure helium atmosphere (1.33 MPa), using a high pressure type TSS HP crystal growth unit [9].The polycrystalline rod was heated by induction at a frequency of 200 kHz. A piece of Mo0701r030 of width 6 mm was inserted in the Mo0771r023 rod and melted. The molten zone was shifted from the bottom to the top of the rod, by lowering the specimen through the working coil. To keep the volume, and hence the composition of the melt constant, the upper shaft had to travel with a greater speed than the lower shaft. The temperature of. the zone was estimated at intervals using a pyrometer. Filings were taken from sections cut at various lengths along the rods and were used for Guinier photographs, using Cu Ka1 (A = 1.5405981 A) radiation and Si (a = 5.43083 A) as internal standard. Some A15-phase was found in all three samples, but sample number 300683 differed markedly from the other samples. This sample was polycrystalline without any single crystals and consisted of A15- and a-phase. In sample number 160683 no a-phase was observed, but it contained a single crystal. The polycrystalline parts consisted

0022-0248/85/$03.30 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

746

R. Koksbang S.E. Rasmussen

/

Growth of Mo

3Ir single crystals

Upper shaft

Mo3 Ir SAMPLE

r~~-~-~-—--—Holder stainless ,IJ ~ steel Split holder boron nitride 00

Counts/lO S

0.,~Fe~d rod Mo0,77 Ir023 Floating zone Mo0,70 1r030 Crystat’Mo3 Ir” Polycrystalline Moo.77 Jr023 Boron nitride holder

100 SINGLE C STAL FWHM~

a

50

Boron nitride support

/INCIDENT V-RAY SHIFT DIRECTION

owersat

~

Fig. 1. Floating zone experiment for growth of Mo3Ir.

of A15-phase and small amounts of MoIr-phase. The same applies for sample number 250583, except that diagrams it also contained someconstant a-phase. of From Guinier the lattice Mothe 3 Jr was determined as a = 4.967 A, with a standard deviation of 0.001 A. Metallographic investigations 3 volume indicated had been that obcrystals of about 10 mm tamed in sample 250583 and 160683. This was corrobated by Laue photographs. A piece (6 mm width) from sample number 160683 was examined by neutron diffraction 98Au radiation withand an by y-ray diffraction using ‘ energy of 412 keV (0.03 A) and a divergence of 2.3 minutes of arc. Fig. 2a shows a y-ray rocking curve of part of this piece which contains a single -

crystal with a mosaicity greater than the resolution of the instrument. The (100) plane was close to being perpendicular to the zone travelling direction. 3 was cut from a A crystal of size 2 X 2 X 1 mm

ROCK! NG CURVE ANGLE (200) REFLECTION Fig. 2. (a) y-Ray rocking curve for a Mo3Ir crystal. (b) Specimen from experiment 160683; the right hand part is a single crystal as evidenced by the rocking curve shown in (a). Radia98Au). Instrumental resolution: 2.3’. tion: 412 keY (0.029 A, ‘

larger crystal from sample 250583 and used for a detailed study using elastic neutron diffraction. TheMostoichiometry of this crystal was determined as 3 251r by X-ray fluorescence analysis. The neutron data also show that the crystal is of good quality as the refinement converged at an R-value Of 1% [10]. The critical temperature for superconductivity was found to be 8.6 that K for single crystal out from the same crystal wasa used for neutron diffraction. An inductive method was used for the 7~measurement [11]. The similarities between Mo 3 Ir and other Al 5 superconductors are subject to further investigations. We are indebted to Mrs. B. Lundtoft for assistance partfor of help the experimental to Mr. M.H. with Nielsen in collectingwork, the neutron

Table 1 Conditions for growth Expt. No.

He gas pressure (MPa)

T (°C)

Power (kW)

Pulling rate Upper shaft

Lower shaft

Composition after zone melting

250583 160683 300683

1.33 1.33 1.33

2100 2090 2030

13.2 13.9 14.3

1,0 1.4 1,2

0,8 0,8 1,0

A15+MoIr* a-phase+sing!e crystal A15+MoIr+single crystal A15+ a-phase

The pulling rate is given in mm/h.

R. Koksban& S.E. Rasmussen

data, to the Danish Natural Science Research Council for the four-circle diffractometer, to the Danish Energy Research Establishment, Ris~,for the y-ray diffraction facilities and to Carlsbergfondet for providing a spark cutting machine. References [1] R.D. Blaugher, R.E. Hem, J.E. Cox and R.M. Waterstraat, J. Low Temp. Phys. 1 (1969) 539. [21 B.T. Matthias and T.H. Geballe, Rev. Mod. Phys. 35 (1963) 1. [31E. Raub, Z. Metallk. 45 (1954) 23. [4] Si. Mmchalik and J.H. Brophy, Trans. Met. Soc. AIME 227 (1963) 1047.

/

Growth of Mo

3Ir single crystals

[51B.C.

747

Giessen, U. Jaehnigen and N.J. Grant, J. Less-Common Metals 10 (1965) 147. [61F.A. Shunk, in: Constitution of Binary Alloys (McGrawHill, New York, 1969) p. 459. [71W.F. Moffat, in: The Handbook of Binary Phase Diagrams, Yols. 1—3 (General Electric Company Corporate Research and Development Technology Marketing Operation, 120 Erie Boulevard, Schenectady, NY 12305, 1978). [8] S.E. Rasmussen, Acta Chem. Scand. A31 (1977) 79. [91R.A. Castonguay, Technical Specialities and Services Co., P.O. Box 9, Salem, MA 01970, USA. [10] R. Koksbang, S.E. Rasmussen and R.G. Hazell, Acta Cryst., submitted. [11] A.N. Christensen, S.E. Rasmussen and G. Thirup, J. Solid State Chem. 34 (1980) 45.