engleski

Impedance spectroscopy: a powerful method for analysis of electrical processes in lithium tungsten phosphate glass-ceramics

Impedance spectroscopy (IS) – a popular tool for analysis of electrical properties allows detailed investigation of composite materials like glass- ceramics. Notably, it enables the analysis of electrical response of every component within the composite. In this work IS is used for detailed analysis of complex mixed ion-polaron glass-ceramics. Glass-ceramics, Li50W@600 and Li50W@800, were prepared by heat- treatment of the starting bulk 5Li2O-5ZnO- 40P2O5-50WO3 (in mol%) glass at 600 ˚C and 800 ˚C for 6 hours. Analysis of IS results provided a detailed insight into changes of DC conductivity and relaxation processes based on the of Zʺ(ω) and Mʺ(ω) spectra in a wide frequency (0.01 Hz – 106 Hz) and temperature (303 K – 513 K) range. Structure and morphology of prepared materials were studied by powder X- ray diffraction (PXRD) and scanning electron microscopy (SEM). PXRD diffractograms showed that after heat-treatment of starting glass, Li50W@600 remained amorphous, while Li50W@800 contained two polymorphs of W2O3(PO4)2, orthorhombic and monoclinic. This was in accord with SEM analysis which showed sporadically distributed dendritic crystallization on the surface of Li50W@600, while SEM of Li50W@800 confirmed massive crystallization with some residual amorphous phase. IS measurements revealed that DC conductivity values of prepared glass-ceramics and the parent glass are within the same order of magnitude which indicates that the formation of W2O3(PO4)2 polymorphs does not impede predominantly polaronic electrical transport. Further, Zʺ(ω) and Mʺ(ω) spectra of Li50W@600 show practically overlapped peaks suggesting a single bulk response. On the other hand, Li50W@800 spectra show three distinct maxima in Zʺ(ω) and one slightly broadened peak in Mʺ(ω) spectrum. This indicates four distinct processes contributing to the total electrical conductivity which are related to the glass matrix, both crystallized polymorphs and grain boundary.

Impendance spectroscopy ; Glass-ceramics ; Electrical properties

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