High-entropy columbites: structure, optical and electrical properties

A high-entropy composition (Mg0.2Zn0.2Ni0.2Co0.2Mn0.2)Nb2O6 with a columbite structure and its Ti-substituted composition (5%) were synthesized. The synthesis was carried out using a modified method of combustion solutions followed by high-temperature sintering. X-ray analysis and scanning electron microscopy were used for characterization of the ceramics. According to diffuse reflectance spectra, the band gap of direct electronic transitions was calculated (Egdir ≈ 2.98–3.05 eV). Solid solutions are characterized predominantly by electronic conductivity. Substitution of niobium cations with titanium leads to an increase in conductivity by 1.2 orders of magnitude in the temperature range 160–750°C.