Electrical properties of rare earth based tungsten bronze vanadates

Barium based tungsten bronze (TB) oxides having high dielectric constant and low loss, can be effectively used as transducers, actuators, capacitors and also in memory devices. All these characteristics stimulated the researchers to replace toxic and hazardous lead based materials by barium based TB materials from industry. In the present research work, polycrystalline samples of Ba4SrRTi3V7O30 (R=Dy, Sm, La) were synthesized by a high temperature solid state reaction technique. Preliminary structural (X-ray diffraction) analyses of these compounds showed the formation of single-phase orthorhombic structures at room temperature having average crystallite size of the order of some nanometer for all the compounds. The scanning electron micrographs (SEM) provided information on the quality of the samples and showed more or less homogeneous distribution of grains over the entire surface of the samples. Detailed dielectric study in a wide temperature range (30–500 °C) showed ferro to para phase transition for Dy and Sm substituted samples whereas no such transition was observed for La substituted samples. Both the grain and grain boundary resistances exhibited negative temperature coefficient of resistance behavior much like semiconductors. The dc conductivity of all the compounds obeyed Arrhenius relation.