Some Combinations of Third-Order Elastic Constants for Strontium Titanate Single Crystals

Abstract

Three linear combinations of the six adiabatic third-order elastic constants in cubic crystals can be determined by use of the ultrasonic second-harmonic generation technique. The combinations which are obtained are designated K3[100], K3[110], and K3[111]. In the work reported here, room-temperature values of the K3's have been measured for strontium titanate single crystals. The reported values are (in units of 1012 dyn/cm2): K3[100]=C111=−49.6±4.3K3[110]=14(C111+3C112+12C166=−27.3±3.2K3[111]=19(C111+6C112+12C144+24C166+2C123+16C456=−27.9±2.6.The data have been compared with the theoretical values of K3 for the alkali halide crystals, and it has been observed that the ratio of | C111 |/C11 for strontium titanate agrees with the corresponding ratio for many of the NaCl type crystals. In order to estimate the six third-order elastic constants of strontium titanate, it has been assumed that the Cauchy relations extended to third-order elastic constants hold.