Ab Initio Prediction of the Redox Potentials of 3d Transition Metals Embedded in a Semiconducting Host Lattice

Here, we report a theoretical investigation devoted to the ab initio determination of the redox potentials E(D n+/D n+1) of a dopant D in a given host lattice. The knowledge of these potentials is of capital importance to anticipate its attainable oxidation states (vs. the synthesis conditions). Hereafter, the host lattice has been selected to be the well-known rutile TiO2 compound because of its interest for many applications, the simplicity of its crystal structure, and a large number of already collected data. Dopants are 3d transition metals (i.e., V, Mn, Fe, Ni, and Cu) substituting titanium atoms. First-principles methods combined with the SCAN functional were used to determine the electronic properties of the doped materials considering the supercell approach. The stability of point defects (intrinsic and extrinsic) at different charge states is discussed based on the estimation of their defect formation enthalpies, and the associated charge transition levels are calculated and positioned in the gap of the undoped material.