Chemical inhomogeneity in the near-surface region of KTaO3 evolving at elevated temperatures

Measurements by x-ray diffraction, secondary ion mass spectrometry and atom ic force microscopy are reported for single crystalline KTaO3 after thermal treatment under oxidizing conditions in the temperature range of 700 to 11 00 degrees C. The formation of a series of new phases KO*(KTaO3)(n) of Rudd lesden-Popper type is observed. Atomic force microscopy of (100) surfaces r eveals corresponding dramatic changes in the surface morphology. Secondary ion mass spectrometry gives evidence of a redistribution of material leadin g to an enrichment of K with respect to Ta close to the surface and a corre sponding depletion in deeper parts of the nearsurface region. The results a re in strong contrast to standard point defect models. Instead, our experim ental observations have to be interpreted in terms of an evolving chemical inhomogeneity due to segregation processes in the near-surface region of th e crystals and intergrowth of KO, which results in the formation of the Rud dlesden-Popper phases. The additional effect of K2O evaporation above 900 d egrees C is discussed and the corresponding topographical changes induced a re documented.