Preparation and electrical properties of semiconducting Ba3−xLaxCe3Ti5Nb5O30 (x = 0.5, 1.0 and 1.5) compounds

Ba3−xLaxCe3Ti5Nb5O30 (x = 0.5, 1.0 and 1.5) compounds were prepared by the solid state reaction of the constituent oxides. They all have the same tetragonal tungsten bronze (TTB)-type structure as shown by XRD and they show semiconducting behaviour (if other rare earths are used in place of cerium, the compounds are insulators as reported earlier). Increasing the amount of La3+ causes only a moderate increase in electrical conductivity of the compound and a decrease in the activation energy of the current carriers. The electrical conductivity at 300 °C for x = 0.5 is 4.26 × 10−4 S/cm and for x = 1.5, it is 9.14 × 10−4 S/cm. Activation energy of the current carriers is 0.364 eV for x = 0.5 and 0.345 eV for x = 1.5. It is possible that La3+ incorporated in the lattice has two effects, as a donor dopant in place of Ba2+ and in creating Ba2+ vacancies. The grain morphology of the dense ceramics observed by means of scanning electron microscopy is also presented.