The Temperature Dependence of Elastic Constants and Zener Anisotropy in Single Crystal KTaO₃ below Room Temperature

We present the first experimental report of the complete elastic tensor of incipient ferroelectric KTaO3 between 9.6 and 307 K, using resonant ultrasound spectroscopy (RUS). The elastic constants C-11 and C-44, as well as the bulk and shear moduli increase roughly linearly upon cooling. Deviations from such dependence are a result of impurities. Zener anisotropy factor is 0.697 at room temperature and decreases to 0.627 at 9.6 K, indicating increasing elastic anisotropy. The temperature dependence of C-12 is anomalous with no stiffening on cooling, which could be a result of different defect species influencing C-12 but not the other constants, possibly due to defect anisotropy. The values of elastic constants and anisotropy are compared at room temperature and below 10 K with the literature reporting experimental results and density functional theory calculations.