Restructuring of the surface region in SrTiO3

 The combination of x-ray diffraction analysis with surface sensitive techniques reveals a chemical inhomogeneity in the surface region of monocrystals of SrTiO₃ prepared under low and high partial pressure of oxygen at elevated temperatures. A solid state reaction leads to the formation of a multilayer-type structure. For oxidized crystals we observe AO-rich Ruddlesden-Popper phases at the surface and Magnelli phases of Ti in deeper layers of the surface region. The order of the layered structure is reversed for the reduced crystals with Ti-oxides of different oxidation levels at the surface and Ruddlesden-Popper phases in lower parts of the surface region. It is argued that this restructuring influences the electrical properties of SrTiO₃. Received: 12 July 1996/Accepted: 24 July 1996