新化合物——Sr_2CaMoO_6的相变与晶体结构

PHASE TRANSITION AND CRYSTAL STRUCTURE OF A NEW COMPOUND ——Sr_7CaMoO_6

本文用差热分析、X射线物相分析及点阵常数的精确测定等方法研究了新化合物Sr_2CaMoO。的相变,证明该化合物在(767±5)℃存在一级位移型相变。低温相α-Sr_2CaMoO。属正交晶系,空间群为Pmm2,室温时点阵常数为:α=8.1933,b=5.7611,c=5.8410。测量密度Dm=4.97g/cm^3,单位晶胞内具有2个化学式量。高温相β-Sr_2CaMoO。属于立方晶系,空间群为Fm3m,在800℃时的点阵常数为a=8.281,Z=4,计算密度Dx=4.76g/cm^3。 本文还用X射线多晶衍射方法分别测定了上述a-Sr_2CaMoO。和β-Sr_2CaMoO的晶体结构,并讨论了结构的特征和影响相变温度的因素。

A new compound Sr2CaMoO6 has been synthesized by solid stare sintering. The phase transition of this compound was investigated by means of DTA, X-ray powder diffraction, precise measurement of lattice parameters and other methods. It is discovered that the compound has a displacive phase transition of the first order at (767±5)℃. The low temperaiure phase, or Sr2CaMoO6, belongs to orthorhombic system, with space group Pmm2, its lattice parameters at room temperature are:a = 8.1933A, b = 5.7611A and c=5.8410A, the measured density is Dm= 4.97g/cm3, and each unit cell contains two formula weight. The high temperature phase, β-Sr2CaMoO6, belongs to the cubic system, with space group Fm3m and the lattice parameter is α = 8.281A at 800℃; Z = 4. The calculated density is Dx= 4.76g/cm3. The crystal structures of α Sr2CaMoO6 and β-Sr2CaMoO6 was also determined by means of the X-ray polycrystal diffraction method. The character of the structure and the factors influencing phase transition temperature are discussed.