Structural, dielectric and impedance properties of NaCa2V5O15 ceramics

Polycrystalline sample of NaCa2V5O15 (NCV) with tungsten bronze structure was prepared by a mixed oxide method at relatively low temperature (i.e. 630 degrees C). Preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Microstructural Study showed that the grains are uniformly and densely distributed over the Surface of the sample. Detailed studies of dielectric properties showed that the Compound has dielectric anomaly above the room temperature (i.e. 289 degrees C), and shows hysteresis in polarization study. The electrical parameters of the compound were studied using complex impedance spectroscopy technique in a wide temperature (23-500 degrees C) and frequency (10(2)-10(6) Hz) ranges. The impedance plots showed only bulk (grain) contributions, and there is a non-Debye type of dielectric dispersion. Complex modulus spectrum confirms the grain contribution only in the compound as observed in the impedance spectrum. The activation energy, calculated from the ac conductivity of the compound, was found to be 0.20-0.30 eV. These values of activation energy suggest that the conduction process is of mixed type (i.e. ionic-polaronic). (C) 2008 Elsevier B.V. All rights reserved.