Characterization of Elastic Constants of Langatate Single Crystals with 32 Symmetry Using Ultrasonic Pulse-Echo Technique

In this study, the propagation of plane waves in the lanthanum gallium tantalate (langatate, LGT) single crystals is investigated. Moreover, the flight time of different waves in the LGT rectangular parallelepiped sample is measured using the ultrasonic pulse-echo (UPE) technique, and the elastic constants of the LGT sample are determined. The experimental results clearly show echoes corresponding to the longitudinal and transverse waves along the x-axis. The waves along the z-axis have a similar property. However, the waves along the y-axis are more complex than those along the x- and z-axes. The echoes corresponding to the quasi-longitudinal waves along the y-axis are clear, but those corresponding to the transverse and quasi-transverse waves along the y-axis are not. The elastic constant can be accurately determined if the wave echoes corresponding to this constant propagate without distinct distortion and are clear; otherwise, it may be impossible to accurately determine the constant using UPE. All elastic constants $c_{ij}^E$ except $c_{13}^E$ of the LGT single crystals can be determined using UPE from one sample. This study uses UPE to provide a reference for the characterization of elastic constants of piezoelectric crystals with 32 symmetry from one sample.