Changes in the crystal structure and dielectric properites of the complex perovskite Sr(Ga0.5Ta0.5)O3 with A-site cation substitution

A-site cation substitution with Ba2+ or Ca2+ ions was made for the complex perovskite Sr(Ga0.5Ta0.5)O-3 phase to modify its dielectric properties. The largely sized Ba2+ ions could be incorporated in the A-site sublattice up to 55 mol% without cation ordering. On the contrary, the A-site Sr2+ ions were completely replaced by the Ca2+ ions. The crystal symmetry of the (Sr, Ca) (Ga0.5Ta0.5)O-3 perovskites correspondingly changed from cubic to orthorhombic with increasing Ca content. Partial B-site cation ordering occurred when 10-50 mol% Ca2+ ions were incorpolated in the A-site Sr2+ ions. The A-site cation substitution caused a very slight change in dielectric constant (epsilon(r)) at microwave frequencies, suggesting a little effect of the substitution on the ionic polarization of the perovskite structure. A substantial lowering in microwave Q-value observed for the solid solutions containing 10-20 mol% Ba2+ or Ca2+ ions might be related to the lack of long-range structure ordering. Temperature coefficient of epsilon(r) at 1 MHz changed from positive high values of the Ca2+-containing perovskites to nearly zero for compounds with 20-40 mol% Ba2+ ions. This change was discussed in relation to the structual strain of (Ga, Ta)O-6 octahedra in the compounds.