複合ペロブスカイトSr(Ga_<0.5>Ta_<0.5>)O_3のA-サイトイオン置換に伴う結晶構造と誘電特性の変化

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A-site cation substitution with Ba^<2+> or Ca^<2+> ions was made for the complex perovskite Sr(Ga_<0.5>Ta_<0.5>)O_3 phase to modify its dielectric properties. The largely sized Ba^<2+> ions could be incorporated in the A-site sublattice up to 55 mol% without cation ordering. On the contrary, the A-site Sr^<2+> ions were completely replaced by the Ca^<2+> ions. The crystal symmetry of the(Sr, Ca)(Ga_<0.5>Ta_<0.5>)O_3 perovskites correspondingly changed from cubic to orthorhombic with increasing Ca content. Partial B-site cation ordering occurred when 10-50 mol% Ca^<2+> ions were incorpolated in the A-site Sr^<2+> ions. The A-site cation substitution caused a very slight change in dielectric constant(ε_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% Ba^<2+> or Ca^<2+> ions might be related to the lack of long-range structure ordering. Temperature coefficient of ε_r at 1 MHz changed from positive high values of the Ca^<2+> -containing perovskites to nearly zero for compounds with 20-40 mol% Ba^<2+> ions. This change was discussed in relation to the structual strain of(Ga, Ta)O_6 octahedra in the compounds.
社団法人日本セラミックス協会の論文
1998-07-01