First-Principles Study on the Photocatalytic Performance of K(Ta_0.5Nb_0.5)O₃ Doped with Metals (Cd, Sn, Hf)

Based on the excellent performance of the K(Ta_0.5Nb_0.5)O₃ (KTN) system, this study systematically investigated the mechanism of the influence of metal element (Cd, Sn, Hf) doping on the photocatalytic performance of KTN ferroelectric materials using the density functional theory (DFT) based on first principles. The findings indicate that after metal atom doping, the tolerance factor of doping systems is similar to that of pure KTN crystals, confirming that doping does not compromise its structural stability. However, the ion radius differences caused by doping lead to lattice distortion, significantly reducing the bandgap width. Because the impurity element substituting the Ta site exhibits a lower valence state compared to Ta, holes become the majority carriers, thereby endowing the semiconductor with p-type characteristics. These characteristics effectively suppress electron-hole recombination while enhancing electron transitions. Furthermore, the increase in the dielectric constant of the doped system indicates an enhancement in its polarization capability, which is accompanied by a significant improvement in carrier mobility. The peak of the imaginary part of the dielectric function and the peak of the absorption spectrum both shift towards the low-energy region, indicating that doping has expanded the light response range of the system. Moreover, the effective mass of the holes in all doped systems is significantly higher than that of the electrons, further demonstrating that the introduction of impurities is conducive to hindering the separation of photogenerated electron-hole pairs. These modifications significantly enhance the photocatalytic performance of the systems.