Structural and impedance spectroscopic study of Zn-substituted Ba5CaTi2Nb8O30 tetragonal tungsten bronze ceramics

Abstract

Zn-doped tungsten bronze compounds derived from Ba5CaTi2Nb8O30, with Ba5CaTi2−xZnxNb8O30 composition (x = 0; 0.04 and 0.08) were synthesized by the conventional solid-state reaction route. Both solubility of Zn in Ba5CaTi2Nb8O30 and tungsten bronze formation with the P4bm space group were verified by the Rietveld method using X-ray diffraction data. The average crystallite size was of the order of 0.08 µm according to Scherrer's formula. SEM micrographs of Ba5CaTi2−xZnxNb8O30 ceramics showed high densification, low porosity, thus a homogeneous grain distribution of different sizes over the entire surface. The average grain size was in the range of 1.3–1.6 µm. The frequency-dependent electrical properties were analyzed by complex impedance spectroscopy. Different types of studies such as the Nyquist plot, real and imaginary part of the impedance, conductivity, modulus formalism, and charge carrier activation energy were used to explain the microstructure-electrical properties relationships.