Preparation, In-situ Phase Characterization And Ferroelectric Mechanism Of Perovskite-type Titanates

Perovskite-type titanates have attracted much attention in the modern scientific research and been widely used in the industry due to their special electrical, optical, and magnetic properties. For the titanate-based ferroelectrics, they exhibit excellent ferroelectric and piezoelectric properties at the morphotropic phase boundary (MPB). Recently there have many investigations on the BiMeO3-PbTiO3 based compounds because they possess high Curie temperature. It has been found that the ferroelectric and piezoelectric properties show a dependence on different BiMeO3 components. In the present investigations, we have found that the ferroelectric performance of the BiMeO3PbTiO3 compounds is related to the average radius of B-site cations of BiMeO3, and these properties are enhanced with increasing value of the tolerance factor of BiMeO3. Addtionaly, by the substitution of BaZrO3. the antiferroelectric relaxor property is found in BiFeO3-PbTiO3 for the first time, which brings a large-signal d^ (690 pm/V).For the perovskite-type ferroelectric compounds, their macro ferroelectric and piezoelectric properties are contributed from the intrinsic factors of phase structure or lattice strain and extrinsic factors of domain switching or domain wall motion. Here, we have investigated the ferroelectric poling process of the Pb(Zr,Ti)O3 compounds around the MPB by in-situ high energy synchrotron X-ray diffraction (SXRD). It has found that:(1) the change of the phase structure and spontaneous polarization in the tetragonal Pb(Zr,Ti)O3 compound around the MPB can be neglected with various electric field. (2) In the rhombohedral compound, its lattice parameters and spontaneous polarization vary with changing of electric field, exhibiting butterfly curve. It must be noted that the length of Pb-O bonds in the rhombohedral phase changes little. (3) By in-situ SXRD investigations, it suggests that the macro ferroelectric property is mainly originated from the domain wall motion and domain switching, while they move differently with the change of grain orientation. For ferroelectric ceramics, the macro polarization is equal to the local polarization in every grain. Hence the macro polarization of the ceramics is limited by the special grains whose polar vector of domains is at an angle of 54.7°from the direction of the electric field.In order to elaborate the mechanism of excellent ferroelectric and piezoelectric properties of perovskite titanates at the MPB, in-situ SXRD were carried out in the PbZr0.535Ti0.465O3 (PZT53.5) ceramics. A phase transformation from the tetragonal to the single monoclinic phase has been observed in the PZT53.5 ceramics, which occurs easily at low temperature. It is the first time to observe the single monoclinic phase in the ceramic, which much benefits the investigations on the ferroelectric property of the monoclinic phase. Based on the phase structure characterization and texture analysis, it is found that:(1) The polar direction of the monoclinic phase rotates in the{101}pc plane, which is the origination of excellent ferroelectric and piezoelectric properties at the MPB. This phenomenon is consistent with the theoretical calculation. (2) In the [001]pc oriented grains of the monoclinic ceramic, the change of the lattice strain induced by electric field is approximate to that of the measured macro strain. (3) The polarization rotation and domain switching are contributed to the macro ferroelectric property of the monoclinic ceramics. (4) The maximum of macro polarization is limited by the grain orientation, and it is no more than the polarization of [001]pc grains in the ceramics.We suppose that these results of in-situ SXRD investigation on Pb(Zr.Ti)O3 compound around the MPB would be helpful for us to understand the ferroelectric poling mechanism of all perovskite-type ferroelectrics. The experimental evidences would serve as references to the theoretical computations, which would be benefit to design new ferroelectric compounds. In terms of the influence of the grain orientation to the macro ferroelectric properties, it enlightens us to adjust and control the micro structure of ceramics in order to achieve excellent performance in future.