engleski

Electrical transport in mixed ion-polaron glasses

In the last few years, mixed electronic-ionic glasses have been studied extensively due to their potential use as cathode materials for solid state batteries. The transformation of the electrical transport from ionic to polaronic have been investigated in four series of glasses containing WO3/MoO3 and Na+/Li+ ions, namely xWO3–(30−0.5x)Na2O– (30−0.5x)ZnO–40P2O5, xWO3–(30−0.5x)Li2O–(30−0.5x)ZnO– 40P2O5, xMoO3– (30−0.5x)Na2O–(30−0.5x)ZnO– 40P2O5, and xMoO3– (30−0.5x)Li2O–(30−0.5x)ZnO–40P2O5, 0≤x≤60 (mol%). The aim of this study is to analyse the role of structural changes as well as changes in molybdenum and tungsten valence state on origin of electrical transport in these mixed ion-polaron glasses. Raman spectroscopy was used for the structural analysis whereas EPR and SQUID magnetometer were used for the determination of the fraction of tungsten and molybdenum ions in different valance states, W5+/Wtot, and Mo5+/Motot, . Electrical properties of glasses were measured by impedance spectroscopy in the wide frequency and temperature range. Raman spectra exhibit the clustering of WO6 units by the formation of W–O–W bonds in glasses with high WO3 and P2O5 content while the coexistence of MoO4 and MoO6 units is evidenced in glasses containing MoO3. However, for glasses with high MoO3 content no clustering of MoO6 octahedra via Mo– O–Mo bonds was found. The dependence of electrical conductivity on the addition of WO3 and MoO3 shows different behaviour. DC conductivity for WO3 glasses either with Na or Li exhibits transition from ionic to polaronic showing a minimum at about 20 to 30 mol% of WO3 as a results of ion-polaron interactions. On the other hand, DC conductivity is almost constant for the glasses containing MoO3 suggesting a co- existence of two independent ionic and polaronic transport in entire compositional region. Such a behaviour is a result of different structural changes in WO3 and MoO3 glasses. Figure 1 reveals two different behaviour of electrical transport in xWO3– (30−0.5x)Li2O– (30−0.5x)ZnO–40P2O5, and xMoO3– (30−0.5x)Li2O– (30−0.5x)ZnO−40P2O5 glasses. On the basis of this analysis the correlation of the local structure, including variation of coordination and the number density of charge carriers in the present glasses will be discussed in details. This picture of electrical transport in glasses investigated provides a new insight into ion- polaron/structure interactions.

Impedance spectroscopy ; Glass structure ; Mixed ion-polaron glasses ; Electrical conductivity

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