SURFACE RELAXATION, SURFACE RECONSTRUCTION AND SURFACE DYNAMICS CLOSE TO THE ANTIFERRODISTORTIVE PHASE-TRANSITION OF SRTIO3(001) SLABS WITH FREE SRO AND TIO2 SURFACES

We discuss the relaxation, reconstruction and dynamics of both (001) surfaces of SrTiO3 (SrO and TiO2 surfaces) in the framework of shell models. The treatment of the SrO surface (surface I) on the basis of a bulk shell model leads to relaxation- and surface-dynamical results, the former of which are in good agreement with recent LEED measurements. However, for the TiO2 surface (surface II), surface-related changes in the Ti-O short-range interactions have to be introduced in the model in order to obtain agreement with the LEED results, as well as to assure dynamical stability of this surface. The physical reason for these model-changes is that the TiO2 surface truncates the Ti-O octahedra. which results in an electron redistribution at the surface. Both surfaces exhibit soft-mode behaviour which, upon lowering the temperature, leads to surface reconstruction that takes place prior to the antiferrodistortive transition of the bulk.