Investigation of Ac conductivity mechanism and dielectric relaxation of semiconducting neodymium-vanadate nanocomposites: temperature and frequency dependency

Abstract

A few binary nanocomposite systems of the overall composition formula xV2O5–(1-x) Nd2O3 for x = 0.2, 0.4, 0.6 and 0.8 has been synthesized via the rapid cooling process. The identification of crystal morphology, lattice fringes of the nanocrystallites, and the selected area electron diffraction patterns have been carried out using the transmission electron microscopy (TEM). TEM micrographs confirm the nanocrystallite development and amorphous character of the nanocomposites. The ac conductivity has been explored in the frequency window from 42 Hz to 5 MHz and in a wide temperature range. The dependency of ac conductivity spectra on frequency and temperature obey Almond-West formalism and Jonscher’s universal power-law. With an increment in temperature, ac conductivity increases, indicating semiconducting behavior. The power-law exponent (s) values are less than unity and increase in relation to the temperature, suggesting non-overlapping small polaron tunneling (NSPT) is the relevant ac conductivity mechanism. The reducing nature of the ac conductivity activation energy, the activation energy for polaron migration and tunneling distance are responsible for the rising of ac conductivity. The increment in the density of defect states within the mobility gap makes ac conductivity to rise as well. The scaled spectra of ac conductivity prove that conductivity relaxation process is temperature independent but composition dependent. In the electrical conduction process, only 66%–71% of the total charge carriers are involved. The values of dielectric constant (ε/) and dielectric loss (ε//) increase with temperature rise and drop with a rise in frequency. The coinciding scaled complex electric modulus spectra (M/ and M//) point out that the dynamical relaxation mechanism is a non-Debye type and is independent of temperature but depend on composition.