Relaxor-ferroelectric crossover seen via characteristic temperatures of Ba_xSr_1-xTiO₃ ferroelectrics detected by acoustic emission

Ba_xSr_1-xTiO₃ ferroelectrics ceramic with x=70 and 80% have been studied by means of acoustic emission over a wide 0-300°C temperature range and under dc external electric field. All the Curie temperatures T_c, intermediate temperatures T^*, and Burns temperatures T_d have been successfully detected and compared with those previously detected in Ba_xSr_1-xTiO₃ with x=60% and pure BaTiO₃, using the acoustic emission. For all the compounds, the critical end points at which the strains are expected to be largest, have been successfully detected, too. While the T_c linearly increases as x increases, it was established that both the T^* and T_d exhibit nonlinear behavior: they initially decrease, attain the minima near x≈70% and then start to increase and tend to those, corresponding to pure BaTiO₃, as it was previously reconstructed for T_d in BaZr_xTi_1-xO₃ compound [Shvartsman and Lupascu, J. Am. Ceram. Soc. 95, 1 (2012)]. Such a phenomenon is discussed from the viewpoint of the presence of polar nanoregions, intrinsic to pure BaTiO₃ in the paraelectric phase, and it is concluded, that a minimum in both the T^*(x) and T_d(x) dependences points out a range of relaxor-ferroelectric crossovers in Ba-based compounds.