Synthesis, Optical and Electrical Properties of High-Entropy Niobate (Mg0.2Cu0.2Ni0.2Co0.2Zn0.2)Nb2O6 with a Columbite Structure

The high-entropy niobate (Mg0.2Cu0.2Ni0.2Co0.2Zn0.2)Nb2O6 with a columbite structure has been synthesized for the first time by a modified solution combustion method followed by high-temperature sintering. According to the diffuse reflectance spectra, the direct band gap is 3.36 eV. The niobate is characterized by the mixed electronic–ionic conductivity (2.5 × 10–3 S/cm at 750°С) comparable with the conductivity of columbite Mg0.8Cu0.2Nb2O6.