Polymorphic phase transition and morphotropic phase boundary in Ba1−x Ca x Ti1−y Zr y O3 ceramics

This paper deals with Ca and Zr co-doped BaTiO3 (BCTZ(x, y)) (x = 0.1, 0.13, 0.2 and y = 0.05, 0.1, 0.15). These ceramics were prepared using the conventional solid state method. The symmetry, dielectric properties, Raman spectroscopy, ferroelectric behavior and piezoelectric effect were examined. X-ray diffraction (XRD) results display that morphotropic boundary occurs from tetragonal to orthorhombic region of BCZT(x=0.1, 0.2, y=0.05, 0.1) and polymorphic phase transitions from tetragonal to orthorhombic, orthorhombic to rhombohedral regions of BCZT(x=0.13, y=0.1). The evolution of the Raman spectra was investigated as a function of compositions at room temperature, in correlation with XRD analysis and dielectric measurements. We note that the substitution of Ca in Ba site and Zr ions in Ti site slightly decreased the cubic-tetragonal temperature transition (TC) and increased the orthorhombic–tetragonal (T1) and rhombohedral–orthorhombic (T2) temperatures transitions. The ferroelectric properties were examined by a P–E hysteresis loop. The two parameters ΔT1 and ΔT2 are defined as ΔT1 = TC − T1 and ΔT2 = TC − T2, they come close to TC for x = 0.13, y = 0.1, which reveals that this composition is around the polymorphic phase. The excellent piezoelectric coefficient of d33 = 288 pC N−1, the electromechanical coupling factor kp = 40%, high constant dielectric 9105, coercive field Ec = 0.32 (KV mm−1) and remanent polarization Pr = 0.1 (µc mm−2) were obtained for composition x = 0.13, y = 0.1.