STRUCTURAL PHASE-TRANSITION IN GAMO4SE8 AND ALMO4S8 BY X-RAY-POWDER DIFFRACTION
STRUCTURAL PHASE-TRANSITION IN GAMO4SE8 AND ALMO4S8 BY X-RAY-POWDER DIFFRACTION
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DOI：
10.1524/zkri.1992.200.1-2.47
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发表时间：
1992-01-01
影响因子：
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通讯作者：
SERGENT, M
中科院分区：
文献类型：
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作者：
FRANCOIS, M;ALEXANDROV, OV;SERGENT, M
在t1=45(2)K和24(2)K时，GaMo4Se8(I)和AlMo4S8(II)分别从具有有序缺陷尖晶石结构的立方高温变质(300K时的空间群F43mbar，a=10.1747(2)埃(I)，9.7289(2)埃(II))转变为菱面体扭曲的低温变质(R3m，a(Rh)=7.1537(3)埃，6.8500(3)埃(II)，α(Rh)=60.572(5)度，60.374(5)-在10K时为(Ii)度)。通过Rietveld方法从吉涅尔衍射仪上记录的T=300K(I，II)，60K(I)，50K(II)和10K(I，II)的X射线粉末数据中精炼出两种修饰的结构参数。在立方修正中，四面体Mo_4团簇具有43mbar对称性，簇内键长为[Mo-Mo]=2.881(2)埃(I)，2.829(2)埃(II)。在相变过程中，当它们在一个三角形基座上膨胀约0.05埃时，它们的对称性降低到3m。
GaMo4Se8 (I) and AlMo4S8 (II) transform at T1 = 45(2) K and 24(2) K, respectively, from a cubic high-temperature modification with ordered defect spinel structure (space group F43mBAR, a = 10.1747(2) angstrom (I), 9.7289(2) angstrom (II) at 300 K) to a rhombohedrally distorted low-temperature modification (R3m, a(rh) = 7.1537(3) angstrom, 6.8500(3) angstrom (II), alpha(rh) = 60.572(5)-degrees, 60.374(5)-degrees (II) at 10 K). Structure parameters for both modifications are refined by the Rietveld method from X-ray powder data recorded at T = 300 K (I, II), 60 K (I), 50 K (II) and 10 K (I, II) on a Guinier diffractometer. In the cubic modification the tetrahedral Mo4 clusters have 43mBAR symmetry and intracluster bond lengths of [Mo-Mo] = 2.881(2) angstrom (I), 2.829(2) angstrom (II). During the phase transition their symmetry is reduced to 3m as they expand each by about 0.05 angstrom at one of their triangular bases.