Anomalous dispersion of the elastic constants at the phase transformation of the PbMg1/3Nb2/3O3 relaxor ferroelectric

Results of the Brillouin light scattering studies of elastic properties of a relaxor ferroelectric lead magnesium niobate, PbMg1/3Nb2/3O3, crystals in the temperature range from 870 to 30 K are presented. By using the experimental results, temperature dependences of elastic C-11, C-12, and C-44 constants have been built. Analysis of the temperature dependences of elastic constants has revealed anomalies in the vicinity of the Burns temperature (T-B approximate to 620 K) and a suppressed ferroelectric phase transition (T-c approximate to 210 K) that occurs when an external electric field is applied. A comparative analysis of the behaviors of elastic constants at different probe frequencies derived from our Brillouin scattering results and ultrasonic [G. A. Smolenskii et al., Sov. Phys. Solid State 27, 801 (1985)] measurements has been carried out. The remarkable dispersion in the relative variations of elastic C-11 and C-44 constants with decreasing temperature below the transition temperature into a cubic anisotropic phase (T-M approximate to 370 K) has been found. These anomalous elastic behaviors related to three typical transition temperatures are discussed as the peculiar natures of relaxor ferroelectrics.