Phase transition, microstructure and electrical properties of Fe doped Ba0.70Ca0.30TiO3 lead-free piezoelectric ceramics

Abstract

Lead-free piezoelectric ceramics of Ba 0.70 Ca 0.30 Ti 1− x Fe x O 3 ( x =0–0.03) have been synthesized by a conventional solid state reaction method. The influence of Fe content on the microstructure, phase transition, dielectric, ferroelectric, and piezoelectric properties is investigated systematically. The ceramics with x ≤0.02 are diphasic composites of tetragonal Ba 0.80 Ca 0.20 TiO 3 :Fe and orthorhombic Ba 0.07 Ca 0.93 TiO 3 :Fe solid solutions. The tetragonal phase is gradually suppressed as x increases, the ceramic with x =0.03 is found to have diphasic pseudocubic and orthorhombic phases. And the grain size is dependent on Fe content significantly. Introduction of Fe at B-sites improves the densification and decreases the sintering temperature. As x increases from 0 to 0.03, the room temperature relative dielectric permittivity enhances, dielectric loss decreases, and the Curie temperature decreases monotonically from 128 °C to 58 °C. However, the ferroelectricity enhances slightly and reaches the maximum near x =0.005, and then weakens with increasing x . On the other hand, the piezoelectric coefficient ( d 33 ) and the electromechanical coupling coefficient ( k p ) decrease simultaneously with increasing x , whereas the mechanical quality factor ( Q m ) increases significantly. The structure–electrical properties relationship is discussed intensively to give more information on (Ba,Ca)TiO 3 -based lead-free piezoelectric ceramics.