Abstract
Chemically $B$-site disordered ${\text{PbSc}}_{\text{l}/2}{\text{Ta}}_{\text{l}/2}{\text{O}}_{3}$ relaxor crystals have been studied by means of dielectric and acoustic emission methods in the vicinity of ${T}_{m}\ensuremath{\approx}280\text{ }\text{K}$. Along with the intrinsic cubic-to-rhombohedral phase transformation at ${T}_{c}=261\text{ }\text{K}$, a phase transformation at ${T}_{n}=293\text{ }\text{K}$ 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.
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