Structure and ferroelectric studies of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 piezoelectric ceramics

Abstract

We have synthesized and studied the structural and ferroelectric properties of lead-free 0.5(Ba0.7Ca0.3)TiO3–0.5Ba(Zr0.2Ti0.8)O3 ceramics in the temperature region of its ferroelectric transition. The synthesized material showed high dielectric constant, low loss and good pyroelectric figure of merit. From the temperature dependent X-ray diffraction measurements, we determined the tricritical point to be in the temperature range of 303–400K. The dielectric measurements indicate a diffuse ferroelectric phase transition (DPT) around 360K in agreement with the X-ray measurements. We studied the evolution of Raman spectra with temperature to understand the nature of phase transition in BaTiO3 (BTO) and the BCTZO. The results indicates that the transition of ferroelectric–paraelectric state is not sharp as in the case of BTO and the polar state persists through the paraelectric state. In general, our study indicates that there are ferroelectric domains of nanometer size beyond the commonly defined transition temperature. The observation of local piezoelectric hysteresis loop indicated the existence of intrinsic ferroelectric property of the ceramic at the nanoscale. The ceramics exhibited electric field tunable dielectric properties with a tunability of 82% at an applied DC field of 40kVcm−1, low dielectric loss of 0.001 and room temperature pyroelectric coefficient of 6×10−8Ccm−2K−1 and the detectivity of 1.9×10−8Ccm−1J−1; larger than those reported for other BaTiO3-based materials. Overall, our results indicate that BCTZO ceramics with coexistence of rhombohedral–tetragonal phases is a promising candidate for lead-free ferroelectric applications.