Surfaces of bulk oxides

Following a brief overview that illustrates the strong research activity dealing with the surface structures of binary oxide, two issues are addressed herein: the relaxation at oxide surfaces and the surface structure of ternary oxides. As a quite general phenomenon, the compensation of the stress generated by the creation of a surface results in relaxation of interlayer spacings and, in the case of ionic solids, in difference in displacement between anions and cations, the so-called rumpling. Rocksalt oxides are of particular interest in this context because they form a series of compounds of identical structure of which only the cations change. Due to the gradual variation they present over the series, they offer a unique playground for the critical analysis of relaxation and rumpling at ionic surfaces. The many applications of the oxides of perovskite structure require the control of terminations at the atomic scale. Despite puzzling discrepancies in preparation conditions, many SrTiO(100) surface reconstructions—c(4 × 2), c(6 × 2), (5×5 )-R26.6, (13×13 )-R33.7— are reproducibly obtained, leading to a set of structural models. However, the demonstration that strontium and stoichiometry defectsdefect play a direct role in reconstructions questions the present models and challenges the goal of preparation of single-terminated SrTiO(100) surfaces of uniform structure.