The electronic structure and optical properties of Ca3(Mn1−xTix)2O7from first-principle calculations

Abstract

The electronic structure and optical properties of Ca3(Mn[Formula: see text]Ti[Formula: see text]O7 ([Formula: see text], 1/8, 2/8, 3/8, 4/8) were studied by first-principle calculations within the generalized gradient approximation approaches (GGA). The lattice constants of Ca3(Mn[Formula: see text]Ti[Formula: see text]O7 increase with the increase of Ti[Formula: see text] content caused by the substitution of Ti[Formula: see text] with larger ionic radius for Mn[Formula: see text]. Ca3(Mn[Formula: see text]Ti[Formula: see text]O7 is a direct band gap semiconductor, and the band gap ([Formula: see text]) increases with the increase of Ti[Formula: see text] content. From the density of states, the introduction of Ti-3[Formula: see text] states can weaken the effects of Mn-3[Formula: see text] states on the bottom of conduction band and has little influence on O-2[Formula: see text] states on the top of valence band. The introduction of nonmagnetic Ti[Formula: see text] ions can weaken the magnetism of Ca3(Mn[Formula: see text]Ti[Formula: see text]O7. According to the Mulliken population analysis, it is found that the introduction of Ti[Formula: see text] enhances the electronic accepting capacity of oxygen ions and enhances the electronic losing capacity of manganese ions. The bond strength of Ti–O covalent bond is stronger than that of Mn–O covalent bond. Furthermore, the optical properties of Ca3(Mn[Formula: see text]Ti[Formula: see text]O7 was calculated. As Ti[Formula: see text] content increases, the absorption edge of Ca3(Mn[Formula: see text]Ti[Formula: see text]O7 has a blue shift, the static refractive index [Formula: see text] decreases, the static dielectric constant [Formula: see text](0) decreases, the position of loss peak moves to higher energy.