Polymorphic phase transition and morphotropic phase boundary in Ba_(1-x)Ca_xTi_(1-y), Zr_yO_3 ceramics

摘要

This paper deals with Ca and Zr co-doped BaTiO_3 (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=01 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 (T_C) and increased the orthorhombic-tetragonal (T_1) and rhombohe-dral-orthorhombic (T_2) temperatures transitions. The ferroelectric properties were examined by a P-E hysteresis loop. The two parameters ∆T_1 and ∆T_2 are defined as ∆T_1 = -T_C - T_1 and ∆T_2 = T_C - T_2, they come close to T_C for x = 0.13, y = 0.1, which reveals that this composition is around the polymorphic phase. The excellent piezoelectric coefficient of d_(33) = 288 pC N~(-1) the electromechanical coupling factor k_p = 40%, high constant dielectric 9105, coercive field E_c = 0.32 (KV mm~(-1)) and remanent polarization P_r = 0.1 (μc mm~(-2)) were obtained for composition x = 0.13, y = 0.1.