The first-principles calculations of Mg2-xTi1+xO4's novel optical properties

Highlights: • Novel optical properties of Mg_2-xTi_1+xO₄ were investigated by the DFT. • Replacing Mg by Ti ions influences the intensity of the Ti-O hybridization. • The Ti-O hybridization has an obvious influence on the electronic transition. • Novel optical properties come from the transition between O 2p and Ti 3d states. Based on the density functional theory (DFT) method, we theoretically studied the novel optical properties of Mg_2-xTi_1+xO₄ (x = 0, 0.25, 0.5, 0.75) through the first-principles calculations. Electronic structures including bond lengths, band structures and density of states (DOS) were calculated to characterize the optical properties. In fact, Mg_2-xTi_1+xO₄'s optical properties are dominated by the electronic interband transitions between Ti-3d and O-2p states, and this electronic transition is directly related to the intensity of the Ti-O hybridization. With Mg ions replaced by Ti ions, Mg_2-xTi_1+xO₄ transfers from insulator to metal, and the Ti-O bond lengths become longer which implies the Ti-O hybridization becomes weaker. As a result, dielectric peaks and absorption peaks both move to the higher energy region (blue shifts) upon the number of substituted Mg ions increasing.