ION-CHANNEL MATCH IN MIXED ALKALI GLASSES

A model is proposed to account for ionic behavior in mixed alkali glasses, in which ionic sites or pathways are constructed and fixed to be accommodated to thermal migration of majority alkali ions near the glass transition temperature. The Anderson-Stuart theory is discussed and revised to show how the activation energy of migration for an impurity alkali becomes larger than that for a host alkali, whether the impurity alkali is larger or smaller than the host alkali. Thus, the smaller ion in a mixed alkali glass is expected to have a negative activation volume in the absolute reaction-rate theory as experimentally observed in lithium beta-alumina and some other ion-conducting crystals. The abnormal conductivity behavior, the large internal friction peak and the so-called thermometer effect in mixed alkali glasses can be explained well with this model without assuming any special cation-cation interaction.