Crystal structure and dielectric behavior of pseudo-cubic perovskite oxides

Complex perovskites (BaM0.9M′0.1)0.984O3 (M=Ti, Zr; M′=Nb, Ta) were prepared by a solid-state reaction at 1300−1600 °C. High-resolution synchrotron X-ray powder diffraction confirmed that all samples, except for MM′=ZrNb, could form a solid solution single phase. All four samples appear to have empty d bands with optical band gaps wider than 3.2 eV. This suggests that the defects generated by the aliovalent substitutions of M4+/M′5+ were compensated by cation vacancies, not by reduction of the transition metal. In contrast to tetragonal and polar BaTiO3, its derivatives (BaTi0.9M′0.1)0.984O3 (M′=Nb, Ta) were stabilized in a simple cubic average structure (space group Pm View the MathML source3¯m) at room temperature. Such structural and compositional modifications of BaTiO3 led to marked evolution of the dielectric behavior: suppression of the temperature-dependent phase transitions and an increase in the dielectric constant. On the other hand, (BaZr0.9Ta0.1)0.984O3 remained isostructural to BaZrO3 and the dielectric properties remained relatively unchanged.