Resonant Ultrasound Spectroscopy of KTa_1-xNb_xO₃ and K_1-xLi_xTaO₃Ferroelectric Relaxor Crystals

Resonance Ultrasound Spectroscopy (RUS) is a fast and nondestructive method to characterize elastic properties of materials. In this method the investigated sample is almost freely suspended between the excitation and receiving transducers. Scanning the excitation frequency, one can record a resonance spectrum of the sample. Further mathematical modelling allows to determine full set of elastic constants of the material investigated. KTa_1-xNb_xO₃ and K_1-xLi_xTaO₃ relaxor ferroelectrics, due to the relative simplicity of their structure, represent a good test bed for modeling more complicated cases of lead relaxors. These materials are finding applications in the devices of adaptive optics. We apply the method of RUS to determine all independent elements of the elastic stiffness tensor for several crystals of KTa_1-xNb_xO₃ and K_1-xLi_xTaO₃. To ensure convergence to the correct numbers, some of the values were cross-checked by ultrasound pulse-echo probing.