Microchemical homogeneity and quenching-induced property enhancement in BiFeO3–BaTiO3 ceramics

BiFeO3–BaTiO3 (BF-BT) solid solutions are promising as the basis for high temperature dielectric and piezoelectric materials, but their microstructural aspects have received relatively little attention. This study evaluates the influence of different processing procedures on the micro-chemical heterogeneity and functional properties of 0.67BF-0.33BT ceramics prepared by solid state reaction. It is shown that the use of high energy planetary ball milling after calcination is an effective method to improve chemical homogeneity and circumvent the core-shell type features found in conventional vibration-milled materials. BF-BT ceramics prepared by high energy milling exhibit enhanced remnant polarization, piezoelectric charge coefficient and coupling factor values of 0.34C m−2, 105 pC/N and 0.24, in comparison with those of vibration milled materials (0.30 C m−2, 73 pC/N and 0.19 respectively). Further improvements in functional properties were achieved by application of an air quenching process, which also led to an increase of 50 °C in both the Curie point and depolarization temperature; these modifications were correlated with increased structural distortion and volume fraction of the rhombohedral phase. Quenched BF-BT ceramics also exhibited mixed inter- and trans-granular fracture modes, whereas that of the as-sintered materials was predominantly inter-granular.