Anomalous behavior of the acoustic phonon velocity and elastic constants of relaxor ferroelectricPbMg1/3Ta2/3O3

Abstract

The behavior of longitudinal acoustic (LA) and transverse acoustic (TA) phonons in a cubic relaxorPbMg1/3Ta2/3O3 (PMT) ferroelectric has been investigated by Brillouin light scattering. Analysisof the temperature dependences of phonon velocity in the temperature rangefrom 50 to 870 K has revealed anomalies in the vicinity of the Burns temperature(TB≈570 K) for LA phonons and a wide frequency-dependent minimum of the velocitiesof LA and TA phonons in the same temperature region as the dielectricresponse anomaly. Using experimental data, temperature dependences of theC11 and C44 elastic constants have been calculated. The elastic constants have been found to befrequency-independent in the gigahertz range. The results obtained are discussed in theframework of modern ideas on the crystalline lattice dynamics of relaxor ferroelectrics.