Mixed alkali effect in quaternary K2O-Li2O-BaO-B2O3 glasses containing V2O5

DC conductivity and density measurements have been carried out for xK2O-(25-x)Li2O-10BaO-20V2O5-45B2O3 glasses and compared with K2O-Li2O-Fe2O3-B2O3 and K2O-Na2O-Fe2O3-P2O5 glasses. The results showed a pronounced mixed alkali effect (MAE) although polaronic conduction was observed in these glasses. There is a deviation from linearity in lnσ-1/T plots at a certain temperature (Td) at which the transition from polaronic to ionic conduction occurs. The derivative -bar Td/-bar X(X=K2O/(K2O+Li2O)) shows a dramatic change at nearly equal concentrations of alkali oxides and can be taken as a characteristic feature of MAE in these glasses. The type and concentration of both the transition metal and alkali ions as well as the host glass matrix govern how the relative mobilities of alkali ions and polarons suppress one another. Both density and molar volume change linearly with composition in opposite directions