Formation of Solid Solutions in BaTiO<sub>3</sub>-BaNi<sub>1/3</sub>Ta<sub>2/3</sub>O<sub>3</sub> and BaTiO<sub>3</sub>-BaMg<sub>1/3</sub>Ta<sub>2/3</sub>O<sub>3</sub> Systems and Their Dielectric

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  • BaTiO<sub>3</sub>-BaNi<sub>1/3</sub>Ta<sub>2/3</sub>O<sub>3</sub>系およびBaTiO<sub>3</sub>-BaMg<sub>1/3</sub>Ta<sub>2/3</sub>O<sub>3</sub>系における固溶体の生成とその誘電的性質
  • BaTiO3-BaNi1 3 Ta2 3O3ケイ オヨビ BaTiO3-BaMg1 3 Ta2 3O3ケイ ニ オケル コヨウタイ ノ セイセイ ト ソノ ユウデンテキ セイシツ

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Specimens were prepared from BaCO3, TiO2, MgO, NiO and Ta2O5 with high purity. They were finally fired at 1400°C for 10-20 hrs. in air and were left to cool in the furnace. By X-ray powder diffraction analysis for them all of specimens showed single phase patterns with perovskite structure. Their lattice constants calculated from (422) reflections explained that a normal solid solution series was formed within the whole composition range in the system BaTiO3-BaNi1/3Ta2/3O3, however, an abnormal one was obtained in the system BaTiO3-BaMg1/3Ta2/3O3. On the X-ray powder diagrams the super lattice reflections of 1:2 cation order were seen in BaMg1/3Ta2/3O3, whereas they were not clear in BaNi1/3Ta2/3O3.<br>It is assumed that in solid solutions with BaMg1/3Ta2/3O3 contents greater than 50 mole%, one Mg2+ layer and two Ta5+ layers through the octahedrally coordinated positions are alternately stacked along a [111] direction in the perovskite cell and the layers are partially occupied by Ti4+ ions without breaking the layer structure. In solid solutions with BaMg1/3 Ta2/3O3 contents smaller than 50 mole%, as well as in the system BaTiO3-BaNi1/3Ta2/3O3, the arrangements of the cations in the octahedrally coordinated positions are regarded to be at random. Thus the system BaTiO3-BaMg1/3Ta2/3O3 may be considered as a rare case in which a solid solution series could be formed in a relatively wide composition range between a simple perovskite-type compound ABO3 and a complex one A (B′B″)O3 having an ordered arrangement of the composit cations.<br>The observed dielectric properties showed no essential difference between both systems. The peaks of the dielectric constants of the solid solutions did not shift appreciably from 120°C, but their heights were rapidly decreased with increasing contents of BaB1/3Ta2/3O3 (B=Ni, Mg). Above the peak-temperatures the dielectric constants obeyed the Curie-Weiss law. Those dielectric properties are not regarded to be intrinsic to those solid solutions but can be attributable to the precipitated BaTiO3 from the solid solutions in the preparation process. An exponential dependence of the dielectric constants on the content of BaB1/3Ta2/3O3 (B=Ni, Mg) may be explained in an analogous way to the dependence of magnetic permeability on the content of ferromagnetic inclusions dispersed in a nonmagnetic cementing material.

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