Intrinsic Properties of Pure and Mixed Monolayer Oxides in the Honeycomb Structure: M2O3 and MM'O3 (M, M' = Ti, V, Cr, Fe)

The growing interest of modern technologies in oxide materials and the advances in the fabrication and control of ultrathin oxide films raise new questions on how to use cation doping or mixing to engineer the properties of such two-dimensional objects. With a special focus on their intrinsic properties in the absence of interaction with a substrate, we have modeled a series of free-standing pure M2O3 and mixed MM'O-3 compounds (M, M' = Ti, V, Cr, Fe) in two-dimensional honeycomb structures within DFT+U and hybrid approaches. A systematic comparison with their bulk counterparts enabled the identification and discussion of their properties, which are driven by their low dimensionality and peculiar atomic structure. On the one hand, it concerns the mixing-induced changes of cation oxidation states, which are controlled by the structure-dependent characteristics of their band edges. On the other hand, an overall increase of the energetic tendency for cationic mixing in low dimensions is highlighted. This comparison shows that low dimensionality enables stabilization of ternary oxides of compositions and properties with no bulk equivalents, thus of a direct interest for modern technologies.