engleski

Impedance spectroscopy as a powerful tool for studying electrical transport in transition metal oxide (TMO)- phosphate glass-ceramics

In the recent years, constant quest for novel glass and glass-ceramic materials for their target application such as cathode material in Li-ion batteries is present. Special attention has been devoted to lithium iron (vanadate) phosphate glass- ceramics and more recently to pure polaronic glass- ceramics for this purpose. In the present work, the effect of crystallization on electrical transport was studied in glass system with composition 40Fe2O3- 60P2O5 (mol%). This type of glass belongs to a family of oxide glasses with pure electronic conduction which is described by small polaron hopping mechanism. Polaronic transport is mainly controlled by amount of Fe2O3 as transition metal oxide (TMO) and fraction of iron ions in different valence states. Induced and controlled heat-treatment of glass leads to partially and almost fully crystallized glasses. Therefore, our interest was to investigate how induced structural changes affects the electrical transport is studied glass-ceramics. Depending on time and heat-treatment temperature various crystalline phases, embedded in residual glass matrix, were confirmed by XRD and Raman spectroscopy, whereas microstucture was evaluated by SEM. Impact of structural changes on electrical transport was explored in details. This study shows that the evolution of crystallization processes can be followed by impedance spectroscopy in wide frequency and temperature range. Electrical conductivity decreases and achieves its minimum at around 15 wt% of crystallinity. In the next stage, with further increase of the treatment temperature, the conductivity rises as a result of an enhanced crystallinity. IS results nicely show the evolution and formation of crystalline phases in amorphous matrix. Correlation between the shape of the spectra and the nature of the electrical transport in these polycrystalline glass-ceramics was confirmed. Thus, different electrical processes have been identified and analysed in detail by combining various formalisms for presenting the IS results. Contribution of each crystalline phase, glass matrix and grain boundaries to total electrical transport is determined from complex impedance plots by means of equivalent circuit modelling, whereas their activation energies were calculated from spectroscopic plots of the imaginary components M” and Z”. Therefore, this work shows how using impedance spectroscopy the electrical processes present in polaronic glass-ceramics can be identified and completly solved.

Impedance spectroscopy ; Electrical conductivity ; Glass-Ceramic

nije evidentirano