Broadband Dielectric Spectroscopy: Unraveling Na+diffusion and mixed conduction in Na₂O-modified zinc phosphate glasses for electrode material applications

Abstract

The fundamental understanding of electric charge (ion + polarons/electrons) transport and relaxation mechanism is essential for applications in solid state ionics. In present work, to study Na⁺ transport, the electrical conductivity of zinc phosphate glasses modified with Na₂O has been investigated in temperature range 313K and 473K and frequency range of 100 mHz to 1 MHz. The experimental data of Nyquist plots is fitted with appropriate equivalent circuits at different temperatures which reveals presence of mixed conduction (polaronic + ionic) and Na⁺ diffusion (at 50 mol% Na₂O) in studied glass samples. The values of frequency exponent (s) obtained from the fitting of experimental data of the real part of electrical conductivity with Almond–West equation (WAE) have been used to determine the conduction mechanism. The electric transport in studied glasses occurred via correlated barrier hopping and non-overlapping small polaron tunnelling conduction models depending on the glass composition and temperature range of investigation. Electric Modulus studies further supports the assertion of composition and temperature dependent conduction mechanisms. The activation energies determined from conductivity, electric modulus, and impedance measurements are found to be consistent, indicating a good correlation in the study.