High-Pressure Synthesis and the Magnetic Properties of Chromium Diantimonide
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or T4" valence states in dichalcogenides,
chalcopnictides, and dipnictides, respectively. Two types of pressure-induced phase transitions, marcasite (or arsenopyrite) to pyrite and pyrite to marcasite structures, were reported in this family. The former was found in FeSe2, FeTe2, CoTe 2, CuSe2, NiP 2, NAs 2 and described to be due to the effective packing of TX 6 octahedra [3, 4]. The latter case was observed in high-pressure X-ray diffraction study of MnS 2 and MnTe 2 [5-7]. The octahedral coordination of the transition metal atom remains unchanged via theses phase transition. In the binary 3d transition metal - antimony systems, two structural groups, low-coordination group and high-coordination group, are known. CrSb 2, FeSb 2 , CoSb 2, and NiSb 2 crystallize into the marcasite- and/or arsenopyrite-type (low-coordination) structures [1, 2]. MnSb 2, which does not exist in the equilibrium Mn-Sb phase diagram, can be synthesized under high-pressure/ temperature condition of 6 GPa and 650*C and also has the marcasite -type structure [8]. Highcoordination group consists of TiSb, and VSb 2. Both TiSb 2 and VSb2 crystallize into tetragonal CuAl2 -type structure [9]. The occurrence of the CuAl 2-type structure in both compounds is considered to be due to the relatively large size of the transition metal atom as compared with the other group transition elements [9]. Taking into account the size and electronic factors of transition elements, it is clearly seen that CrSb 2 locates the boundary between the low- and high-coordination groups. High-pressure technique would be useful to examine the structural relationship in the transition metal diantimonide family as demonstrated in diphosphides and diarsenides [10]. In this study, high-pressure synthesis of CrSb 2 was examined and a new polymorphic form with the CuA12-type structure was successfully synthesized. This paper describes the results of 139 Mat. Res. Soc. Symp. Proc. Vol. 499 0 1998 Materials Research Society
structural analysis and the electrical and magnetic measurements on the high-pressure form of CrSb 2. EXPERIMENTAL Stoichiometric mixture of chromium and antimony powders was heated at 700*C for 168 h in an evacuated silica tube and quenched to room temperature. The marcasite -type (low-pressure form) sample, thus obtained, was subjected to high-pressure/ temperature condition using the belt-type high-pressure equipment. The detailed cell assemblage of the belt-type equipment is described in our earlier paper [11]. High-pressure/ temperature treatments were carried out at 3-7.7 GPa and 600-650TC for 30 min and then the sample was quenched to room temperature prior to releasing the applied pressure. A new high-pressure form of CrSb 2 was successfully obtained by the reaction at 7-7.7 GPa and 600-650°C. The crystal structure of the high-pressure form was refined by Rietveld analysis of the powder X-ray diffraction data using the RIETAN program [12]. The electrical resistivity and the thermoelectric power were measured by conventional d.c. methods. The magnet
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