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Title: Polar catastrophe and the structure of KTa 1-xNb xO₃ surfaces: Results from elastic and inelastic helium atom scattering

The structure and dynamics of cleaved (001) surfaces of potassium tantalates doped with niobium, KTa 1-xNb xO₃ (KTN), with x ranging from 0% to 30%, were measured by helium atom scattering (HAS). Through HAS time-of-flight (TOF) experiments, a dispersionless branch (Einstein phonon branch) with energy of 13-14 meV was observed across the surface Brillouin zone in all samples. When this observation is combined with the results from earlier experimental and theoretical studies on these materials, a consistent picture of the stable surface structure emerges: After cleaving the single-crystal sample, the surface should be composed of equal areas of KO and TaO₂/NbO₂ terraces. The data, however, suggest that K⁺ and O²⁻ ions migrate from the bulk to the surface, forming a charged KO lattice that is neutralized primarily by additional K⁺ ions bridging pairs of surface oxygens. This structural and dynamic modification at the (001) surface of KTN appears due to its formally charged KO(-1) and TaO₂/NbO₂(+1) layers and avoids a “polar catastrophe.” This behavior is contrasted with the (001) surface behavior of the fluoride perovskite KMnF₃ with its electrically neutral KF and MnF₂ layers.
Authors:
 [1] ;  [2] ;  [2] ;  [2] ;  [2] ;  [2] ;  [2] ;  [3]
  1. Valdosta State Univ., Valdosta, GA (United States)
  2. Florida State Univ., Tallahassee, FL (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Grant/Contract Number:
FG02-97ER45635
Type:
Publisher's Accepted Manuscript
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Volume: 92 Journal Issue: 3; Journal ID: ISSN 1098-0121
Publisher:
American Physical Society
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
OSTI Identifier:
1193911

Flaherty, F. A., Trelenberg, T. W., Li, J. A., Fatema, R., Skofronick, J. G., Van Winkle, D. H., Safron, S. A., and Boatner, L. A.. Polar catastrophe and the structure of KTa1-xNbxO₃ surfaces: Results from elastic and inelastic helium atom scattering. United States: N. p., Web. doi:10.1103/PhysRevB.92.035414.
Flaherty, F. A., Trelenberg, T. W., Li, J. A., Fatema, R., Skofronick, J. G., Van Winkle, D. H., Safron, S. A., & Boatner, L. A.. Polar catastrophe and the structure of KTa1-xNbxO₃ surfaces: Results from elastic and inelastic helium atom scattering. United States. doi:10.1103/PhysRevB.92.035414.
Flaherty, F. A., Trelenberg, T. W., Li, J. A., Fatema, R., Skofronick, J. G., Van Winkle, D. H., Safron, S. A., and Boatner, L. A.. 2015. "Polar catastrophe and the structure of KTa1-xNbxO₃ surfaces: Results from elastic and inelastic helium atom scattering". United States. doi:10.1103/PhysRevB.92.035414.
@article{osti_1193911,
title = {Polar catastrophe and the structure of KTa1-xNbxO₃ surfaces: Results from elastic and inelastic helium atom scattering},
author = {Flaherty, F. A. and Trelenberg, T. W. and Li, J. A. and Fatema, R. and Skofronick, J. G. and Van Winkle, D. H. and Safron, S. A. and Boatner, L. A.},
abstractNote = {The structure and dynamics of cleaved (001) surfaces of potassium tantalates doped with niobium, KTa1-xNbxO₃ (KTN), with x ranging from 0% to 30%, were measured by helium atom scattering (HAS). Through HAS time-of-flight (TOF) experiments, a dispersionless branch (Einstein phonon branch) with energy of 13-14 meV was observed across the surface Brillouin zone in all samples. When this observation is combined with the results from earlier experimental and theoretical studies on these materials, a consistent picture of the stable surface structure emerges: After cleaving the single-crystal sample, the surface should be composed of equal areas of KO and TaO₂/NbO₂ terraces. The data, however, suggest that K⁺ and O²⁻ ions migrate from the bulk to the surface, forming a charged KO lattice that is neutralized primarily by additional K⁺ ions bridging pairs of surface oxygens. This structural and dynamic modification at the (001) surface of KTN appears due to its formally charged KO(-1) and TaO₂/NbO₂(+1) layers and avoids a “polar catastrophe.” This behavior is contrasted with the (001) surface behavior of the fluoride perovskite KMnF₃ with its electrically neutral KF and MnF₂ layers.},
doi = {10.1103/PhysRevB.92.035414},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 3,
volume = 92,
place = {United States},
year = {2015},
month = {7}
}

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