先の速報 (窯協, 74, 335 (1966)) にひきつづき, 炭酸バリウム (BaCO₃) の新準安定相の生成と性質について, X線分析, 熱分析, 電子顕微鏡観測, 熱膨脹, 電気伝導度, 比重, BET面積の諸測定などにより詳細に検討した. BaCO₃に酸化クロム (III) を少量添加して, BaCO₃, のγ(斜方晶)-α(六方晶) 転移温度 (約800℃) で加熱し, 急冷することにより未知の結晶相が生ずる. この新相をδ相と命名した. δ相は酸化クロム (III) の代りに種々のクロム酸塩, 硫酸塩または燐酸塩 (表-1) を用いた場合にも得られる. δ相はこれら添加剤がBaCO₃の結晶転移 (高温型α→低温型γ) 時に固溶したものと考えられ, その比重は4.36で, γ型の4.55よりも低く, イオンの充填率に差異があることを示している. そして, δ相は再加熱, 水との接触, あるいは数分間摩砕することにより容易に室温安定型 (γ) に転移するような準安定的性質をもっている. 双子型微少熱量計を用い, 既知量のδ相粉末を水25ml中に投入することにより求められたδ→γ転移熱量は8.5cal/g-BaCO₃で, γ→α転移熱 (18cal/g) の約1/2に相当することが認められた. また, δ相の示差熱分析曲線には500℃近くに吸熱現象があり, その後, 発熱してγに転相する (図-4). 吸熱異常が, 昇温速度 (図-5), 添加剤の種類 (図-6) に依存しないことなどから, BaCO₃中のCO₃^2-イオンの回転と密接な関係をもっものと考えられた. このことは同時に, δ→γ転移の前後において, 異常な膨脹, 収縮が観測され (図-7), イオンのmigrationによる格子の再編成の過程として理解された.
δ相の水蒸気との接触, 水中浸漬などによるγ相への転移は外形的にも著しい変化が認められ (写真-3, 4, 5), この転移に対する水の砿化作用として, 分子が小さく, かつ, 誘電分極の大きい水がδ相粒子表面に吸着し, Ba²⁺-CO₃^2-イオン間結合力の弛緩をもたらすためと考えた. もちろん, 本質的には, Ba²⁺イオンの分極能が小さいことが原因している.

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For the purpose of getting a better insight into the initial stages of densification during the hot-pressing, the hot-pressing experiments using the compacts of amorphous polystyrene sphere were performed. The size of the amorphous polystyrene plastic sphere was 0.695mm in diameter.
The obtained experimental data showed that the densification curves were divided into three parts. These parts were characterized by an initial rapid densification followed by an intermediate stage such as Murray's relation and finally a much slower process. On the other hand, it has been reported that the rapid densification in the initial stage was attributed to; (a) the particle rearrangement, (b) the influence of the porosity on the applied load, (c) the plastic flow within the solid particle.
To ensure these effects, the creep experiments using the sintered polystyrene sphere compacts which had various porosities were performed. From these experiments, it was found that the visco-elastic deformation within polystyrene itself and the influence of the porosity on the applied load could be effective, the former in paticular. In spite of these facts, the rearrangment of the spheres within the sintered body could not be observed in these experimental conditions. These were the contrast to the reports which had been presented.
In the intermediate stage of densification, Murry's relation was valid for the experimental data. In this stage, it was reasonable that the densification proceeded by the viscous flow characteristics of polystyrene sphere.
The final stage of the densification which was a much slower process was attributed to the pore closure as some investigaters reported.
Besides, the effects of porosity to the creep rate in the sintered polystyrene plastic sphere compacts were determined. As the results, the following experimental equations were obtained.
J/J₀=1+5P
J=J₀ exp 3.7P
J₀: creep compliance for the zero porosity specimen
J: creep compliance for the P % porosity specimen
P: prorosity %

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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-BaNi_1/3Ta_2/3O₃, however, an abnormal one was obtained in the system BaTiO₃-BaMg_1/3Ta_2/3O₃. On the X-ray powder diagrams the super lattice reflections of 1:2 cation order were seen in BaMg_1/3Ta_2/3O₃, whereas they were not clear in BaNi_1/3Ta_2/3O₃.
It is assumed that in solid solutions with BaMg_1/3Ta_2/3O₃ 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 BaMg_1/3 Ta_2/3O₃ contents smaller than 50 mole%, as well as in the system BaTiO₃-BaNi_1/3Ta_2/3O₃, the arrangements of the cations in the octahedrally coordinated positions are regarded to be at random. Thus the system BaTiO₃-BaMg_1/3Ta_2/3O₃ 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.
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 BaB_1/3Ta_2/3O₃ (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 BaB_1/3Ta_2/3O₃ (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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