Topochemical Fluorination and Changes in Electronic Properties of Layered Oxide Single Crystalline Thin Films

Abstract

Layered oxyfluoride single-crystalline thin films of Sr₂RuO₃F₂, Ca₂RuO_2.5F₂, and Sr₂IrO_2.5F₃ were fabricated via topochemical fluorination. All the fluorinated films exhibited an insulating behavior and a largely expanded c-axis than the precursors. Sr₂RuO₃F₂ film was a Mott insulator with Ru^4＋ states and had two inequivalent F^－ sites in the SrO layers. In contrast, Ca₂RuO_2.5F₂ film had the Ru^3＋ state and only one F^－ site in the CaO rock-salt blocks. This discrepancy is probably due to the larger lattice distortion in the Ca₂RuO₄ precursor. The conduction mechanism of Ca₂RuO_2.5F₂ film was described by two-dimensional variable range hopping. The effective total angular momentum J_eff＝3/2 of Sr₂IrO_2.5F₃ film was stabilized upon fluorination owing to the large electronegativity of fluorine. The conduction mechanism of Sr₂IrO_2.5F₃ film was described by Efros-Shklovskii variable-range hopping. These results will be useful for modifying electronic states by anion doping to explore unprecedented electronic properties in layered oxides.