Determination of Layer Structure in Sr1-xLaxTiO3+0.5x (0 < x < 1) Compounds by High-Resolution Electron Microscopy

High resolution electron microscopy has shown that samples of La-substituted SrTiO3 prepared in oxidizing atmospheres contain oxygen-rich layers parallel to a perovskite {110} plane. These layers have the same structure as those found in La2Ti2O7 and explain how the excess oxygen required by the altervalent substitution is incorporated into the structure. At low levels of substitution, layers occurred predominantly in clusters irregularly distributed within the host perovskite. Increasing substitution, and therefore increasing frequency of the layers, led to new ordered compounds corresponding to the n = 4.5 and n = 5 members of the compositional series Srn-4La4TinO3n+2.