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

• Published in: Applied physics letters 2016-11, Vol.109 (20)
• Main Authors: Kim, Dae Su, Cheon, Chae Il, Lee, Seong Su, Kim, Jeong Seog
• Format: Article
• Language: English
• Subjects: Applied physics; Ceramics; Cooling; Cooling effects; Cooling rate; Crystal structure; Diffraction; Diffusion rate; Distortion; Electrical properties; Ferroelectric materials; Ferroelectricity; Phase transitions; Piezoelectricity; Quenching; Temperature; Transmission electron microscopy; X-ray diffraction
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4967742

The effect of the cooling rate on the electrical properties was investigated in the 0.75BiFeO3-0.25BaTiO3 ceramics. The air-quenched samples had superior ferroelectric and piezoelectric properties to the slowly cooled samples. The quenching effect weakened when the quenching temperature was less than 700 °C and eventually disappeared at 500 °C and below. The X-ray diffraction and transmission electron microscopy showed that the cooling rate had a significant effect on the crystal structure and domain structure. The slowly cooled sample showed a very small rhombohedral distortion and a poorly developed domain structure, which leads to weak ferroelectric and piezoelectric properties at room temperature. The quenched and slowly cooled samples had a ferroelectric rhombohedral structure (R3c) at room temperature and a paraelectric cubic structure (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 orthorhombic structure (Amm2). The diffusion of oxygen vacancies in the slowly cooled sample is believed to lead to a more symmetric orthorhombic structure at intermediate temperatures between 500 °C and 650 °C during the slow-cooling process and consequently very small rhombohedral distortion at room temperature.