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RESEARCH PRODUCT

Comparative study of [001] surface relaxations of perovskite titanates

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Surface relaxations of the cubic perovskite SrTiO and BaTiO crystals have been studied in the framework of the shell model. The 33 positions of atoms in several surface layers embedded into the electrostatic field of the remainder of the crystal were calculated. Ti 4q , Sr 2q ,B a 2q and O 2y ions in six near-surface layers are displaced differently from their crystalline sites. Such effects create the so-called surface rumpling, a dipole moment and the electric field in the near-surface region. Calculated atomic displacements were compared with the LEED experimental data and showed good agreement. Our simulations have demonstrated that the cubic perovskite SrTiO crystals 3 reveal surface polarization and accompanied by the presence of relevant electric field. This arises 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 wx imposing a long-range order in paraelectric SrTiO . As discussed in the literature, the 001 surface turns out to be ferroelectric with 3 properties different from the bulk material. q 1998 Elsevier Science S.A.