Electrical conductivities of mixed cation phosphate glasses

Abstract

In order to examine the cause of the mixed alkali effect in phosphate glasses, the electrical conductivities of (33.3- x)Na 2O· xR n O m ·8.4Al 2O 3·58.3P 2O 5 glasses, where R n O m is Li 2O, K 2O, MgO, CaO, and BaO, were measured from room temperature to 400°C. It was found that the mobility of alkali ions of one type decreased whenever they were partially substituted by alkali ions of another type or alkaline earth ions, and that the decrease in the mobility of the alkali ions is not characteristic of mixed alkali glasses but common to mixed cation glasses where alkali ions are substituted by any other cations. The decrease in the mobility can be explained on the basis of the independent-path model in which it is assumed that cations can move only through vacant sites left by those of the same type. Thus the mixed cation effect in phosphate glasses was found to be essentially the same as that in silicate glasses.