Effect of cooling rate on phase transitions and ferroelectric properties in 0.75BiFeO3-0.25BaTiO3 ceramics

The effect of the cooling rate on the electrical properties was investigated in the 0.75BiFeO3-0.25BaTiO3ceramics. The air-quenched samples had superiorferroelectric andpiezoelectric properties to the slowly cooled samples. Thequenching effect weakened when thequenching temperature was less than 700  °C and eventually disappeared at 500 °C and below. TheX-ray diffraction and transmission electron microscopy showed that the cooling rate had a significant effect on thecrystal structure and domainstructure. The slowly cooled sample showed a very small rhombohedral distortion and a poorly developed domainstructure, which leads to weakferroelectric andpiezoelectric properties at room temperature. The quenched and slowly cooled samples had aferroelectric rhombohedralstructure (R3c) at room temperature and a paraelectric cubicstructure (Pm-3m) at temperatures above 650  °C. On the other hand, the slowly cooled sample had a centro-symmetric orthorhombic (Pbnm)structure at intermediate temperatures, while the quenched sample had a noncentrosymmetric orthorhombicstructure (Amm2). The diffusion of oxygenvacancies in the slowly cooled sample is believed to lead to a more symmetric orthorhombicstructure at intermediate temperatures between 500  °C and 650 °C during the slow-cooling process and consequently very small rhombohedral distortion at room temperature.

Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: Dae Su Kim, Chae Il Cheon, Seong Su Lee and Jeong Seog Kim Source Type: research