Acoustic emission pronounced field-induced response near critical point in Ba_0.6Sr_0.4TiO₃ ferroelectrics

Ba_0.60Sr_0.40TiO₃ ceramic ferroelectric (FE) has been investigated in the wide temperature range under a dc external electric field (E) by means of dedicated acoustic emission (AE) method. The Curie point T_c=9°C, as well as both the temperature points, characteristic of relaxor ferroelectrics (RFEs), Burns temperature T _d=283°C and intermediate temperature T*=182°C have successfully been detected. T_c demonstrates a nontrivial behavior in dependence on E, i.e., initially it decreases, reaches a minimum of T _th=1.2°C at the small threshold field E_th=0. 75kVcm^-1, and then starts to increase similar to ordered FEs, as E increases. The AE count rate, accompanying this nontrivial behavior of T _c(E) dependence, exhibits a pronounced maximum ≈5.4s^-1 above E_th at the E_m=1.5kVcm^-1. Both, T _d and T* demonstrate a dependence on E, too, as was recently observed in relaxor FEs PbSc_0.5Nb_0.5O₃ [Dul'kin et al., J. Appl. Phys. 113, 054105 (2013)]. The AE pronounced maximum is explained to be a consequence of the giant piezoelectric coefficients intrinsic to Ba_xSr_1-xTiO₃ FEs.