Surface structure of niobium-doped potassium tantalate KTa_{1 −x}Nb_xO₃obtained from helium atom scattering studies

Abstract

Helium atom scattering experiments have been carried out on the (001) surface of KTaO(3) doped with 6, 10 and 15% Nb, produced by cleaving in situ single crystal samples. Several phenomena were observed through He atom diffraction measurements, including metastable behavior immediately after cleaving, reconstruction of a fraction of the surface to (2 × 1) domains after thermally cycling the surface temperatures, and the distribution of step heights of terraces at the surface as multiples of the unit cell dimension of ∼ 4 Å. In addition, a large hysteresis effect was found in the (100) azimuth in the variation of surface reflectivity with surface temperature; a much smaller hysteresis effect was found in the (110) azimuth. The hysteresis effects appear for all Nb doping concentrations. Finally, small oscillations in the specular and Bragg diffraction intensities near the surface temperature 80 K were also observed.

Polar catastrophe and the structure ofKTa1−xNbxO3surfaces: Resu

“…In all cases for targets with Nb doping levels up to 20%, the Fourier transform of the oscillations in the specular peak intensities revealed that the principal step height between terraces was 4 Å. [7][8][9][10] A step height of 8 Å was also seen in almost all experiments, but with a much smaller probability. A step height of 6 Å with even lower probability was found in only a few experiments.…”

“…[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.…”

“…[33] AD experiments in the FSU HAS laboratory on cleaved, single-crystal KTN targets, in both <10> and <11> high symmetry azimuths, yielded Bragg peaks consistent with the 4 Å surface lattice parameter expected for both KO and TaO 2 /NbO 2 layers. [4][5][6][7] (See Figure 1a.) Hence, the KO surface formed after stabilization appears essentially the same as the KO layer produced by the cleaving. Additionally, it was found that He atom diffraction from cleaved targets which were cooled to temperatures less than 100 K and then warmed above180 K showed small, broad half-order diffraction peaks in addition to the large, sharp integer-order peaks.…”