Tuning electronic structure and optical properties of Ba 0.875 Yb 0.125 TiO ₃ via transition metal substitution: a DFT study

The electronic structure and optical properties (such as the dielectric function, refractive index, absorption and reflectivity) of Cubic BaTiO 3 co-doped with Yb at site A and transition metal elements M (M = Rh, Ru, Zr, Pt, Pd) at site B were studied using the first-principles calculations based on Density Functional Theory (DFT). It is suggested that the energy band gap width increases from 3.15 eV for pure BaTiO 3 (BT) to 3.86 eV for Ba 0.875 Yb 0.125 Ti 0.875 Zr 0.125 O 3 . Impurity levels near Fermi level across Fermi surface were introduced by B-site transition metals (such as Pd, Pt, Rh, Ru, Tc and V) doping in Ba 0.875 Yb 0.125 TiO 3 . The doping system with 12.5% Pd, Pt, Rh and Ru respectively doped at the B site of Ba 7 YbTi 8 O 24 exhibits enhanced reflectivity, reaching up to ~30% at specific visible wavelengths (e.g., 2.5 eV), which represents an increase of 15-30 percentage points compared to pure BaTiO 3 over the 1.6-3.1 eV range. The peak values of the refractive index are enhanced by 10-25%, and the corresponding photon energies are blue-shifted by 0.3-1.2 eV. Transition metal doping increases the static dielectric constant, with the largest value reaching 7.7867 for the Pt-doped system, a ~27% increase over the pure phase (6.13).