Polar catastrophe and the structure of $\mathrm{KT}{\mathrm{a}}_{1-x}\mathrm{N}{\mathrm{b}}_x{\mathrm{O}}_3$ surfaces: Results from elastic and inelastic helium atom scattering

Journal Article · Mon Jul 13 00:00:00 EDT 2015 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PhysRevB.92.035414· OSTI ID:1265599

Flaherty, F. A. ^[1]; Trelenberg, T. W. ^[2]; Li, Jiefang A. ^[2]; Fatema, R. ^[2]; Skofronick, J. G. ^[2]; Van Winkle, David H. ^[2]; Safron, Sanford A. ^[3]; Boatner, Lynn A. ^[4]

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1. Valdosta State Univ., Valdosta, GA (United States). Dept. of Physics
2. Florida State Univ., Tallahassee, FL (United States). Dept. of Physics
3. Florida State Univ., Tallahassee, FL (United States). Dept. of Chemistry and Biochemistry
4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

In this paper, 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 13-14meV 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 O^2- 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.” Finally, this behavior is contrasted with the (001) surface behavior of the fluoride perovskite KMnF₃ with its electrically neutral KF and MnF₂ layers.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1265599
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 92, Issue 3; ISSN 1098-0121
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
potassium tantalate
singlecrystal
KTN