COMPARATIVE-STUDY OF [001] SURFACE RELAXATIONS OF PEROVSKITE TITANATES

Surface relaxations of the cubic perovskite SrTiO3 and BaTiO3 crystals have been studied in the framework of the shell model, The positions of atoms in several surface layers embedded into the electrostatic fie ld of the remainder of the crystal were calculated. Ti4+ Sr2+, Ba2+ an d O2- ions in six near-surface layers are displaced differently from t heir crystalline sites. Such effects create the so-called surface rump ling, a dipole moment and the electric field in the near-surface regio n. Calculated atomic displacements were compared with the LEED experim ental data and showed good agreement. Our simulations have demonstrate d that the cubic perovskite SrTiO3 crystals reveal surface polarizatio n and accompanied by the presence of relevant electric field. This ari ses due to a disturbed force balance accompanying the surface creation and affect 5-6 planes below the surface. In other words, the surface can serve as important factor imposing a long-range order in paraelect ric SrTiO3. As discussed in the literature, the [001] surface turns ou t to be ferroelectric with properties different from the bulk material . (C) 1998 Elsevier Science S.A.