采用 WinTA 100热膨胀仪研究了四方黄铜矿 CdGeAs2晶体在320~620 K 温度范围内的热膨胀行为,探索了CdGeAs2晶体热膨胀各向异性的物理机制。测定晶体a轴和c轴方向的热膨胀系数αa和αc发现,αa>>αc>0,表现出强烈的各向异性热膨胀特性。利用最小二乘法,拟合出CdGeAs2晶体的晶格常数(a, c)与温度(T)的函数关系式,与文献报道值吻合。分别计算出不同温度下的四方畸变因子δ=2–c/a, Cd-As 键长(lCd?As)和 Ge-As 键长(lGe?As)以及相应的热膨胀系数αCd?As和αGe?As。结果表明, a、c、δ、lCd?As、lGe?As和αCd?As均随着温度的升高而增大, c/a和?Ge?As则随着温度的升高而减小。当T=360 K时,αCd?As是αGe?As的6.36倍,是造成CdGeAs2晶体强烈热膨胀各向异性的主要原因。
Thermal expansion measurements by WinTA 100 on tetragonal chalcopyrite cadmium germanium arsenide (CdGeAs2) crystal were carried out in the temperature range between 320 K and 620 K. Based on these measurements, the mechanisms of thermal expansion anisotropy is proposed. It is found that the axial thermal expansion coefficients (αa and αc) are both positive, and ??>>??, which exhibits anisotropic thermal behavior intensively. By the least squares method, the functional relationship between structural parameters (a, c) and temperature (T) is set up, which are coincident with published literature. Furthermore, the tetragonal distortion δ=2–c/a, the interatomic distances (lCd?As and lGe?As) and the bond expansion coefficients (αCd?As and αGe?As) are calculated at different temperatures, respectively. Simultaneously, it is also found that a, c,δ, lCd?As, lGe?As, and αGe?As increase with temperature increase, while c/a and αGe?As are just the opposite. When T=360 K, ?Cd?As is 6.36 times of αGe?As. Hence, the difference between αCd?As and ?Ge?As is the main reason for the significant anisotropy of thermal expansion.
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