Influence of sintering temperature on microstructure of Na0.5Bi0.5TiO3 ceramics

Na0.5Bi0.5TiO3 (NBT)-based compositions are among the most promising lead-free ferroelectrics. Although studies of modification of NBT-based compositions' properties are a hot topic, there has been very little attention paid to their characterization from the standpoint of ceramics and the process of producing them. Here, we report on comprehensive analysis of the influence of sintering temperature across a wide temperature range (1020–1240 °C) on the complete microstructure and chemical content of NBT ceramics produced by solid state sintering, which is dominating in producing of NBT ceramics. Thorough attention is paid to the grain size distribution, porosity, and inhomogeneity. It is demonstrated how the grain size distribution monotonously becomes more diffuse and the average grain size increases, upon sequential increasing of the sintering temperature. Along with high density (reaching 98% of the theoretical value), two types of pores are observed. Macroscopic pores form at high sintering temperatures along with a small concentration of residual pores remaining after densification of ceramics and observed throughout the whole range of sintering temperatures. Two types of inclusions are detected, corresponding to the chemical compositions NaBiTi6O14 and TiO2, as inferred from local energy-dispersive X-ray analysis. Non-intentional non-stoichiometry is not detected in the matrix grains of the NBT ceramics, even if sintered at high temperatures. It is inferred that, instead of changing the composition of the matrix grains, Na and Bi volatilization rather influences the porosity and inhomogeneity of NBT.