CdGeAs2晶体的热膨胀行为研究

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α_a和α_c发现, α_a>>α_c>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(l_Cd-As)和 Ge-As 键长(l_Ge-As)以及相应的热膨胀系数α_Cd-As和α_Ge-As。结果表明, a、c、δ、l_Cd-As、l_Ge-As和α_Cd-As均随着温度的升高而增大, c/a和α_Ge-As则随着温度的升高而减小。当T=360 K时,α_Cd-As是α_Ge-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 Behaviors of CdGeAs2 Crystal

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 (α_a and α_c) are both positive, and α_a>>α_c, 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 (l_Cd-As and l_Ge-As) and the bond expansion coefficients (α_Cd-As and α_Ge-As) are calculated at different temperatures, respectively. Simultaneously, it is also found that a, c, δ, l_Cd-As,l_Ge-As, and α_Ge-As increase with temperature increase, while c/a and α_Ge-As are just the opposite. When T=360 K, α_Cd-As is 6.36 times of α_Ge-As. Hence, the difference between α_Cd-As and α_Ge-As is the main reason for the signi?cant anisotropy of thermal expansion.