c軸配向アパタイト型ケイ酸ランタン多結晶体の作製と酸化物イオン伝導

抄録

We have successfully prepared the three types of highly c-axis-oriented polycrystalline materials of lanthanum silicate apatite（La_9.33Si₆O₂₆, La_9.50Si₆O_26.25 and La_9.50Si_5.87O₂₆）by isothermal heating of the diffusion couples consisting of La₂SiO₅ and La₂Si₂O₇ at 1873 K for 50-100 h. The resulting polycrystals were subsequently characterized using polarizing microscopy, X-ray diffration and impedance spectroscopy. The annealed couples were mechanically processed, and the thin-plate electrolytes consisting of the grain-aligned polycrystals were obtained. The oxide-ion conductivity along the c-axis of oxygen hyper-stoichiometric apatite, La_9.50Si₆O_26.25,was ca. 2.5 times higher than that of oxygen stoichiometric apatite, La_9.33Si₆O₂₆, at 723-973 K. The polycrystalline material of Si-deficient apatite, La_9.50Si_5.87O₂₆, showed, among the three types of apatite polycrystals, the highest conductivity above 850 K; the conductivity at 873 K was 4.2×10⁻² S/cm.