Effect of Germanium Substitution on the Structure and Ionic Conductivity in Hexagonal Perovskite Derivative Compound Ba3WVO8.5

Abstract

A series of hexagonal perovskite derivative compounds Ba3WV1-xGexO8.5-x/2 (x = 0, 0.1, 0.2, 0.3) was synthesized using solid-state reaction route. Phase-purity and structure of all the samples were determined by Rietveld refinement of powder X-ray diffraction data. All the samples were found to have rhombohedral lattice (space group: R3 @#x0305;m), and a systematic increasing trend in unit cell parameters with increasing Ge4+ content was observed. High temperature X-ray diffraction studies on the samples confirmed their stability up to 1023 K. Temperature and frequency dependent dielectric studies indicated high ionic conduction in all these samples and a systematic enhancement in ionic conductivity with increasing Ge4+ incorporation. Among the studied samples, the Ba3WV0.7Ge0.3O8.5 composition showed the highest dc conductivity (~ 1.80 × 10-5 S/cm at 973K). The enhancement in conductivity on incorporation of Ge4+ ions was attributed to the ease diffusion of oxide ions in the lattice due increasing unit cell volume and oxygen ion vacancies. The temperature evolution of ionic conductivity in the samples showed Arrhenius behaviour and the activation energies were in the range of 0.9 to 1.5 eV. In addition, a changeover conduction mechanism was observed at higher temperature. The shape parameters in the electrical modulus spectra were determined using H-N function fitting and it was found that the distribution of relaxation times increased with Ge4+ content, which could be due to opening of more paths and modes for diffusion of ions.