The 1×1/1×2 phase transition of the TiO 2( [formula omitted]) surface––variation of transition temperature with crystal composition

Abstract

We use low-energy electron diffraction and low-energy electron microscopy (LEEM) to show that the TiO 2(1 1 0) surface can reversibly transform between a high-temperature 1×1 phase and a low-temperature 1×2 phase. We find that the 1×1/1×2 transition occurs for a range of stoichiometry in oxygen-deficient crystals. To be quantitative about the stoichiometry dependence of the transition temperature, we accurately measure the crystal stoichiometry by using LEEM to determine the temperature at which crystallographic shear planes disappear from the bulk. In this way we show that the transition temperature increases with decreasing bulk oxygen content. By applying the Claperyon equation, we argue that this temperature dependence implies that the 1×1 and 1×2 surface phases have significantly different stoichiometries, with the 1×2 phase being Ti-rich compared to the 1×1 phase.