Phase evolution in (1−x)(Na_0.5Bi_0.5)TiO₃-xSrTiO₃ solid solutions: A study focusing on dielectric and ferroelectric characteristics

In the present work, the nature of phase evolution of (1−x)(Na_0.5Bi_0.5)TiO₃-xSrTiO₃ (NBT-xST) solid solutions with x of 0–0.6 is revealed by characterizing the dielectric and ferroelectric properties. Two unique dielectric anomalies associated with high-temperature nanoregions (PNRs) in the ergodic relaxor (ER) state and low-temperature PNRs in the nonergodic relaxor (NR) state are identified. Characteristic temperatures, including T_B, T_RT∗, T_m, T_d and T_T∗, are determined in fresh and poled states on the basis of the characteristics of the evolution of these two dielectric anomalies. The whole evolution of the transition from the NR state to the ER state is reflected by the temperature-dependent polarization versus electric field (P-E) hysteresis loops, i.e., from the square loops, via the double-like loops, to the slim loops. The characteristic temperatures, including T_P-N, T_N-R and T_R-dis, are determined by the characteristics of the evolution of P-E loops. Accordingly, a phase diagram of NBT-xST was constructed according to these characteristic temperatures. Most importantly, the relationship between polarization responses and heterogeneous polar phase coexistence has been established and a schematic diagram is given. This work will help to understand the phase evolution and its impact on the macroscopic properties of NBT and the associated NBT-based solid solutions.