High-Entropy Columbites: Structure, Optical and Electrical Properties

A high-entropy compound (Mg_0.2Zn_0.2Ni_0.2Co_0.2Mn_0.2)Nb₂O₆ with the columbite structure and its Ti-substituted (5%) composition were synthesized for the first time. The synthesis was carried out using a modified method of solution combustion followed by high-temperature sintering. The samples were examined using the methods of X-ray diffraction analysis and scanning electron microscopy. The band gap of direct electronic transition (\(E_{{\text{g}}}^{{{\text{dir}}}}\) ≈ 2.98–3.05 eV) was calculated using the diffuse reflectance spectra. The solid solutions are characterized by predominantly electronic conductivity. The substitution of titanium cations for niobium cations leads to an increase in the conductivity by 1.2 orders of magnitude in the temperature range of 160 to 750°C.