Synthesis and Electrical Properties of Cation Deficient Perovskite-type Oxides in the Ln-A-Ti-Al-O System (Ln=La, Nd; A=Ca, Sr).

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The effects of ion vacancy on the crystal structure and the electrical conductivity of perovskite-type oxides were investigated. The cation and oxide ion deficient perovskite-type oxides LnA_2-x, Ti₂AlO_9-d, (Ln=La, Nd; A=Ca, Sr) were synthesized. Single-phase samples of LnA_2-xTi₂AlO_9-d were prepared by heating at 1673 K in air in the compositional range of x=0-0.3 for both A=Ca and Sr. The crystal structures were cubic perovskite-type for A=Sr and orthorhombic perovskite-type for A=Ca. Lattice parameters of LnA_2-xTi₂AlO_9-d, increased with increasing amounts of A cation vacancies. All the samples exhibited semiconducting behavior in the temperature range of 573-1023 K in air. The measurements of conductivity for LnA_2-xTi₂AlO_9-d as a function of oxygen partial pressure revealed n-type conductivity at oxygen partial pressure less than 0.21 atm. The conductivities of LnA_2-xTi₂AlO_9-d, increased with increasing amount of A cation and oxide ion vacancies for both A=Ca and Sr.