Polarity compensation mechanisms on the perovskite surface KTaO<sub>3</sub>(001).
basic_science · Level V
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- Record sourced from PubMed, PMID 29420289.
- Also identified by DOI 10.1126/science.aar2287.
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Abstract
The stacking of alternating charged planes in ionic crystals creates a diverging electrostatic energy-a "polar catastrophe"-that must be compensated at the surface. We used scanning probe microscopies and density functional theory to study compensation mechanisms at the perovskite potassium tantalate (KTaO<sub>3</sub>) (001) surface as increasing degrees of freedom were enabled. The as-cleaved surface in vacuum is frozen in place but immediately responds with an insulator-to-metal transition and possibly ferroelectric lattice distortions. Annealing in vacuum allows the formation of isolated oxygen vacancies, followed by a complete rearrangement of the top layers into an ordered pattern of KO and TaO<sub>2</sub> stripes. The optimal solution is found after exposure to water vapor through the formation of a hydroxylated overlayer with ideal geometry and charge.