Evidence of local anisotropic strains in relaxor ferroelectrics below intermediate temperature T^* detected by acoustic emission

Oriented {100}-, {110}-, and {111}-cuts of Pb_0.78Ba _0.22Sc_0.5Ta_0.5O₃ single crystals have been studied by means of the acoustic emission (AE) method during their thermal cycling in the temperature range of 300-600K. For all crystal orientations pronounced AE signals have been detected near 490K, which corresponds to the intermediate temperature T^*. However, the highest AE count rate has been detected from {110}-oriented cuts, revealing strong anisotropic coupling between the existing polar species that at T ^* merge into larger regions of polarization (PNRs). The temperature's hysteresis is revealed to be 15K, indicating that the transformation processes at T^* can be considered as local Martensitic-like ferroelectric transitions inside PNRs. The interplay between PNRs and ultrahigh local strains of perovskite-type relaxor ferroelectrics is discussed.