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Title: Polar catastrophe and the structure of KTa1-xNbxO₃ surfaces: Results from elastic and inelastic helium atom scattering

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.
 [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:
OSTI Identifier:
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Publisher's Accepted Manuscript
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 92; Journal Issue: 3; Journal ID: ISSN 1098-0121
American Physical Society
Sponsoring Org:
Country of Publication:
United States