Effect of heat-treatment mechanism on structural and electromechanical properties of eco-friendly

Lead-free piezoelectric ceramics, (Bi.sub.0.70Ba.sub.0.35)(Fe.sub.0.65Ti.sub.0.35)O.sub.3 (BBFT), were fabricated via a solid-state reaction method and then treated using different heat-treatment processes (furnace cooling, air quenching (AQ), and water quenching). In all these ceramics, the X-ray diffraction analysis revealed morphotropic phase boundaries between the rhombohedral and tetragonal phases. Changes in the average grain size, relative density, and electrical properties in the BBFT-AQ composition were observed. For the optimum BBFT-AQ ceramic, significantly enhanced dynamic (d.sub.33* ~ 340 pm/V) and static (d.sub.33 ~ 165 pC/N) piezoelectric coefficients were obtained. Moreover, the d.sub.33* increased to 40% (d.sub.33* ~ 475 pm/V) with increasing temperature from 25 °C to 75 °C upon the application of a 4.0 kV/mm electric field. The related defect states were established by the variation in the transition of Fe.sup.3+ to Fe.sup.2+ and O.sub.V or [Formula omitted] concentration observed using X-ray photoelectron spectroscopy analysis. These factors are directly related to the electromechanical response enhancement in the BBFT piezoceramics. This study provides a paradigm for a deeper analysis of particular scientific heat-treatment mechanisms and the enhancement of functional properties in BBFT ceramics.