Structural investigations on ferroelectric Pb_1−3/2xLa_xTiO₃ using the x-ray Rietveld method

The structures of the defect perovskite Pb_1−3/2xLa_xTiO₃ prepared by the solid-state method were investigated in the solubility range of 0.05 ⩽ x ⩽ 0.30 with 0.05 increment by x-ray Rietveld method. In the system Pb_1−3/2xLa_xTiO₃, the atom displacements of Ti (δ_Ti) and Pb/La (δ_Pb/La) along the spontaneous polarization (P_s) direction (c axis) decrease nonlinearly with increasing La content, while the value of δ_Ti/δ_Pb/La decreases linearly. The shape of oxygen octahedron of compounds Pb_1−3/2xLa_xTiO₃ is independent of the La content. The calculated value of P_s decreases linearly in the solubility range of 0.05 ⩽ x ⩽ 0.30. In the refinement process, the hkl dependence of diffraction line broadening was also taken into account. The anisotropy of microstrain-like broadening observed in Pb_1−3/2xLa_xTiO₃ might be ascribed to occurrence of compositional inhomogeneity between the crystallites.