X-ray study of the deficient perovskite La _{2 3}TiO₃

The A-site deficient perovskite La _{2 3}TiO₃ was synthesized under the controlled atmosphere of CO₂H₂ mixed gas at 1350°C, and the structure was investigated by the powder X-ray diffraction method. The product is slightly oxygen deficient (La _{2 3}TiO_3-λ, where 0.007 ≦ λ ≦ 0.079), and the structure is dependent on λ: when λ is small, the perovskite cell is distorted to orthorhombic symmetry and the unit cell is doubled along the c′ (> b′, a′) axis, while a cubic perovskite structure is facilitated with the increase of λ. A structural model, which calls for an ordered arrangement of the A-site vacancies along the c′-axis, is proposed and its order parameter is calculated from the intensities of the superstructure lines.