Electrical transport in iron phosphate glass-ceramics

Abstract

In this study, the effect of crystallization on electrical transport in iron phosphate glass with composition 40Fe2O3-60P2O5 (mol%) was investigated. This type of glasses exhibits the electronic conduction which is described by polaronic conduction mechanism. Induced and controlled heat-treatment of 40Fe2O3-60P2O5 glass leads to partially and almost fully crystallized glass-ceramics. The influence of heat-treatment temperature on structural changes, the appearance of crystalline phases, their interactions and influence on electrical transport were studied in details.Depending on heat-treatment temperature various phases, such as Fe3(P2O7)2, Fe4(P2O7)3 and Fe(PO3)3, embedded in glass matrix, were confirmed by powder X-ray diffraction (XRPD) and Raman spectroscopy (RS), whereas thermally induced microstructural changes were evaluated by high-resolution transmission electron microscopy (HR-TEM).Impact of the structural changes on the electrical properties was explored by means of impedance spectroscopy (IS) in wide frequency and temperature range. DC conductivity decreases in the first stage of the crystallization process and achieves its minimum. With further increase of the heat-treatment temperature, the electrical conductivity rises as a result of an enhanced crystallinity. IS results show the evolution of crystallization and formation of crystalline phases in glassy matrix. Correlation between the shape of the spectra and the nature of the electrical transport was confirmed. Different electrical processes have been identified by detail analysis and contribution of each crystalline phase, glass matrix and grain boundaries to total resistance/conductivity is determined by complex impedance plots by means of equivalent circuit modeling.