Theoretical and experimental investigation of the electronic, optical, electric, and elastic properties of Zn-doped anatase TiO₂ for photocatalytic applications

Abstract

Anatase titanium dioxide is one of the most promising energy materials. However, it suffers from low electrical conductivity due to its wide band gap that corresponds to only UV radiation absorption. Regarding these challenges, Zn doping is considered as an attractive solution to enhance its performance in photocatalysis, solar cells, and transparent conducting oxide films. Thus, with this motive, we have investigated Zn-doped titanium dioxide (Zn:TiO₂) by ab initio calculations within the density functional theory (DFT). The theoretical RAMAN spectra are calculated using the Becke three-parameter Lee–Yang–Parr (B3LYP) functional through the implementation algorithm of the CRYSTAL17 code. Results agree well with the experimental data, and the observed modes reveal the anatase phase of TiO₂. The increase in Zn content leads to a band gap reduction, and the optical properties are strongly enhanced in TiO₂: Zn (4 and 6%), which extend light absorption edge to the visible light range and promote good photocatalytic activity. Correlations between DFT calculations and electrical response are also established. Accordingly, the values of the capacitance as well as resistance are extracted from the equivalent circuit model of the Nyquist plots. The resistance decreases with increasing the Zn content which results in higher leakage current under constant voltage stress. The mechanical response is also investigated to verify the stability of the (Zn:TiO₂) films. In the tetragonal structure, pure TiO₂ has a large bulk modulus of 178 GPa and a small shear modulus of 71.8 GPa. However, with increasing the Zn concentration, the stiffness and brittleness of the films decrease, while the anisotropic character increases. This could be very promising for energy-related applications.