Phase transformation above T_m in PbSc_0.5 Ta _0.5 O₃ relaxor as seen via acoustic emission

Chemically B -site disordered PbSc_l/2 Ta_l/2 O ₃ relaxor crystals have been studied by means of dielectric and acoustic emission methods in the vicinity of T_m ≈ 280 K. Along with the intrinsic cubic-to-rhombohedral phase transformation at T_c =261 K, a phase transformation at T_n =293 K is evidently detected by acoustic emission. Under an external dc electric field T_c gradually increases with increasing the field, whereas T_n exhibits nontrivial behavior, namely, initially decreases and then starts increasing, similarly to T_c. The characteristic temperature T_n is attributed to the occurrence of incommensurate modulated antiferroelectric regions, which have previously been suggested to coexist with both the cubic paraelectric and rhombohedral ferroelectric phases in the vicinity of T_m. The nontrivial behavior of T_n under an external dc electric field is also discussed.