Polarity compensation mechanisms on the perovskite surface KTaO 3 (001)

• Published in: Science (American Association for the Advancement of Science) Vol. 359; no. 6375; pp. 572 - 575
• Main Authors: Setvin, Martin, Reticcioli, Michele, Poelzleitner, Flora, Hulva, Jan, Schmid, Michael, Boatner, Lynn A, Franchini, Cesare, Diebold, Ulrike
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science (AAAS) 02.02.2018
• Subjects: MATERIALS SCIENCE
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.aar2287

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 ) (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 stripes. The optimal solution is found after exposure to water vapor through the formation of a hydroxylated overlayer with ideal geometry and charge.