Phase transition temperature and electrical properties of (Bi1∕2Na1∕2)TiO3–(Bi1∕2A1∕2)TiO3 (A=Li and K) lead-free ferroelectric ceramics

Abstract

( 1 − x ) ( Bi 1 ∕ 2 Na 1 ∕ 2 ) Ti O 3 – x ( Bi 1 ∕ 2 Li 1 ∕ 2 ) Ti O 3 and (1−x)(Bi1∕2Na1∕2)TiO3–x(Bi1∕2K1∕2)TiO3 (abbreviated as BNLT100x and BNKT100x, respectively) ceramics were prepared by the conventional ceramic fabrication process. In this study, the depolarization temperature Td, rhombohedral-tetragonal phase transition temperature TR-T, and the temperature of the maximum dielectric constant Tm were determined from the temperature dependences of the dielectric and piezoelectric properties. The results showed that Td of BNLT100x and BNKT100x increased to 199 and 209°C, respectively, at the rhombohedral composition. In addition, we revealed that Td is related to the magnitude of the rhombohedrality 90-α and the tetragonality c∕a. We studied the piezoelectric properties in detail, and the relationship between Td and piezoelectric properties was clarified. Moreover, we discussed the ferroelectricity of the middle phases of Td−TR-T and TR-T−Tm.