Characteristic temperatures of PbFe_1/2Nb_1/2O₃ferroelectrics crystals seen via acoustic emission

PbFe1/2Nb1/2O3 ferroelectrics crystals have been investigated using an acoustic emission. All the characteristic points have been detected: the Néel antiferromagnetic–paramagnetic phase transition at 158.6 K, both the rhombohedral–tetragonal at 363–348 K and tetragonal–cubic at 382–365 K structural phase transitions, the intermediate temperature T* at 431–427.5 K and the Burns temperature Td, extending through 564–603 K. It is shown that a dielectric response is unable to locate the Td correctly, but both the thermal expansion and acoustic emission are able. Acoustic emission is found to be more powerful for T* than for Td, which is usually observed in some well known relaxor ferroelectrics. Such a phenomenon is discussed from a viewpoint of dynamics of polar nanoregions.