Surface structure and dynamics ofKTaO3(001)

Abstract

Elastic and inelastic helium atom scattering experiments have been carried out on the KTaO 3 (001) surface, prepared by cleaving in situ under ultra high vacuum conditions. Several unusual observations were recorded in the helium diffraction studies. These include the appearance of metastable surface features immediately after cleaving ͑which decay to the stable (1ϫ1) surface after a few hours͒, the formation and dissolution of small (2ϫ1) and (1ϫ2) domains depending on the thermal history of the surface, large hysteresis in the diffraction beam intensities measured for surface temperatures between 200 K and 50 K depending on whether the surface is being warmed or cooled, and permanent changes in the diffraction intensities as a result of poling normal to the surface plane. The single-phonon energy-transfer experiments yield three surface phonon dispersion branches in the ͗100͘ and ͗110͘ high-symmetry azimuths. Calculations of the lattice dynamics using the VASP approach are described and the results are compared with the measurements.

Polar catastrophe and the structure ofKTa1−xNbxO3surfaces: Resu

“…[6,34] They found, first, that electron transfer occurs from surface oxygens to subsurface tantalums so that the average formal charge of a surface KO is reduced from -1 to -½. They also obtained a slight relaxation of the surface oxygens that leads to additional stabilization.…”

“…[5] The helium atom scattering (HAS) laboratory group at FSU has investigated cleaved (001) perovskite surfaces, particularly potassium tantalate (KTaO 3 ) [6], and potassium tantalate doped with Nb (KTN) [7][8][9] or lithium (KLT). [9,10] When cleaved, the fresh surfaces are nominally composed of layers, KO/LiO and TaO 2 /NbO 2 , that are formally charged -1 and +1, respectively.…”

“…[27] The FSU HAS laboratory has employed low-energy helium atom scattering to investigate the structure of (001) surfaces of potassium tantalate doped to various levels with niobium, KTa 1-x Nb x O 3 (KTN), with x ranging from 0 to 30%, through angular distributions (ADs) and drift spectra (DS) experiments. [4][5][6][7] The experimental techniques have been described in detail in previous articles from this laboratory. [6,7] Briefly, ADs are measurements of the intensity of the elastically scattered He atoms as a function of scattering angle.…”

“…[4][5][6][7] The experimental techniques have been described in detail in previous articles from this laboratory. [6,7] Briefly, ADs are measurements of the intensity of the elastically scattered He atoms as a function of scattering angle. They reveal diffractive interference in the atom scattering due to the periodic surface structure.…”

“…They also obtained a slight relaxation of the surface oxygens that leads to additional stabilization. Further calculations [6] showed that extra K + ions can be stably bound to the surface oxygens, with the most stable arrangement having a K + ion bound between two oxygens as a bridge in a <10> or <01> direction. The calculated normal vibrational frequency of this ion corresponds to a phonon mode with energy of 12.8meV.…”