Effects of Ca substitution on structure, piezoelectric properties, and relaxor behavior of lead-free Ba(Ti0.9Zr0.1)O3 piezoelectric ceramics

Abstract

Lead-free piezoelectric (Ba1−xCax)(Ti0.9Zr0.1)O3 (BCTZ-x, x=0, 0.05, 0.10, 0.15, 0.20) ceramics are synthesized via a conventional solid state reaction method. The effects of Ca substitution on the microstructure, dielectric properties, piezoelectric properties, and relaxor behavior of BCTZ ceramics were systematically investigated. Structural characterization of the synthesized BCTZ shows that a structure with morphortropic phase boundary (MPB) between rhombohedral phase and tetragonal phase at about x=0.15 has been obtained. The (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 ceramics exhibit the most homogeneous microstructure with the largest grains. The dielectric and piezoelectric properties are found to be enhanced near the phase transition composition due to the lattice distortion caused by Ca2+ substitution. The dielectric relaxor behavior of the BCTZ ceramics was enhanced with increasing Ca content. The relaxor nature of the BCTZ ceramics may be attributed to the formation of polar clusters induced by local distortion. The increased relaxor behavior in the BCTZ ceramics also contributes to the improvement of the piezoelectric properties. The (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 ceramic exhibits optimum properties with a dielectric constant, ε3T/ε0, of 5800, piezoelectric constant, d33, of 350pC/N, d31 of −122pC/N, electromechanical coupling factor, kp, of 33%, and k31, of 16%, indicating that the (Ba,Ca)(Ti,Zr)O3 ceramic is a promising candidate for lead-free piezoelectric materials.