Dielectric and optical properties of Ba5AFe0.5Ta9.5O30 (A = K, Li) tungsten bronze ceramics

Two novel Ba5AFe0.5Ta9.5O30 (A = K, Li) ceramics were fabricated through a conventional solid-state sintering process. Both samples were paraelectric phase with tetragonal tungsten bronze structure at room temperature. Dielectric response of the samples was studied by using AC impedance spectroscopy and universal dielectric relaxation law in detail. Dielectric relaxation at high temperatures is attributed to the oxygen vacancies induced by the evaporation of alkali oxide. The relaxation activation energy of the ceramics is lower than half of the band gap Eg obtained by UV–Vis spectroscopy, which resulted from the emergence of oxygen vacancies at high temperatures. In the visible light region, the samples showed strong absorption with a band gap of about 2.7 eV, which could be applied as a visible light irradiation photocatalyst.