Studying Elastic Constants of Potassium Lithium Tantalate using Ultrasonic Pulse Echo Probing

Ferroelectrics are characterized by spontaneous polarization appearing at critical temperature T_c. In some materials, called relaxors, polarization appears over a range of temperatures around T_c. Such materials are particularly interesting for numerous applications from capacitors and memory storage to actuators and nanopositioning. Many aspects of the relaxor ferroelectricity phenomenon are still unclear. One of the representatives of such materials is K_1-xLi_xTaO₃ (KLT). We report on the study of temperature dependences of c₁₁ elastic constants in several KLT crystals with x = 0.01, 0.1, and 0.2 using ultrasound pulse echo technique in the temperature range of 65 – 300 K. By shooting an ultrasound pressure pulse and recording its echoes, we determine the speed of compressive wave, which is related to the c₁₁ constant. The relaxor transition is marked by significant anomalous softening of the c₁₁ in the neighborhood of T_c.