Grain size effect-induced evolution of relaxor state, domain structure, and polarization in Bi0.5Na0.5TiO3-based ceramics

Abstract

The grain size effect on relaxor state, domain structure, and electric field-induced polarization in Bi_0.5Na_0.5TiO₃ (BNT)-based ceramics is studied using a paradigmatic system. The average grain size increases from 0.50 to 1.90 μm when sintering temperature (T_s) is elevated from 1050 to 1200 °C. All the ceramics have a similar phase structure, while domain width increases from dozens of nanometers to > 100 nm, and more grains show an obvious domain morphology with increasing grain size. Three stages of relaxor state and polarization evolution are observed. At T_s = 1050 ℃ (0.50 μm), a low polarization response and unobservable relaxor-ferroelectric transition indicate the weak ferroelectric correlation due to the quite small grains. At T_s = 1100–1150 ℃ (0.91–1.27 μm), an enhanced polarization and obvious relaxor-ferroelectric transition & domain switching are observed. At T_s = 1170–1200 ℃ (1.44–1.90 μm), the squared ferroelectric loops with high polarization and enhanced depolarization temperature are shown, demonstrating that only the large grains can stabilize the ferroelectric correlation and promote a high polarization. This work reveals the significant grain size effect of relaxor state and electric field-induced polarization in BNT-based ceramics.