X-ray diffraction study of BaTi0.65Zr0.35O3 and Ba0.92Ca0.08Ti0.75Zr0.25O3 compositions: influence of electric field

The BaTi0.65Zr0.35O3 and Ba0.92Ca0.08Ti0.75Zr0.25O3 compositions of the BaTiO3–BaZrO3–CaTiO3 system have been studied by X-ray diffraction on unpoled and poled ceramics. The dielectric peak of BaTi0.65Zr0.35O3 at Tm=200 K (1 kHz), characteristic of a relaxor behaviour, does not correspond to a symmetry change of the structure. Such a result was already reported for the well-known ferroelectric relaxor PbMg1/3Nb2/3O3, but unlike this latter case, an electric field (≤9.6 kV cm−1) cannot induce a long-range polar order. This point is discussed. Ba0.92Ca0.08Ti0.75Zr0.25O3 behaviour is similar to those of Pb(Mg0.3Nb0.6Ti0.1)O3, PbSc1/2Nb1/2O3 or PbSc1/2Ta1/2O3 relaxor lead-based perovskites. It undergoes a zero-field rhombohedral phase transition. It transforms spontaneously from a relaxor into a macroscopic ferroelectric state upon cooling. The transition temperature Tc=208 K, determined by the fit of the spontaneous deformation, is in good agreement with the dielectric and pyroelectric measurements.