Cubic to pseudo-cubic tetragonal phase transformation with lithium and beryllium doping in CaTiO3 and its impact on electronic and optical properties: a DFT approach

First-principles calculations, with CASTEP code, were employed to study the effect of lithium (Li) and beryllium (Be) doping on structural stability, phase transformation, electronic band structure and optical characteristics of CaTiO3. The substitution of Ca-atoms with the Li- and Be-atoms changes the lattice parameters and hence unit cell volume and consequently the electronic band structure of CaTiO3 is modified. With 12.5% Li- and Be-doping, we observed a structural phase transformation from cubic to pseudo-cubic tetragonal structure which is in good agreement with the literature. The impact of structural phase transformation on the electronic band structure has been explained with the help of total, partial and elemental partial density of states. In case of Li-doping, the value of band gap slightly increases from 1.866 to 1.964 eV while the band gap value decreases to 1.614 eV for Be-doping. In both cases of doping, maxima of valence band are shifted from R to Z symmetry point whereas the minima of conduction band remain at G symmetry point. In pure and doped cases, the nature of the band gap remains unaltered, i.e., indirect band gap. From optical response of the doped compounds, we perceive a red shift in the absorption. With Be- and Li-doping, the static refractive index also increased from 2.48 to 2.63 and 4.1, respectively. The change in electronic structure and optical characteristic with Li- and Be-doping would make this compound a suitable candidate for future optoelectronic devices.