THE MIXED-ALKALI EFFECT AND THERMODYNAMIC STATE OF GLASSES

The mixed alkali effect, a pronounced reduction in electric conductivi ty when two or more dissimilar alkali ions coexist, is most conspicuou s under a d.c. electric field while it diminishes under high frequency . Correspondingly, low d.c. conductivity of the mixed alkali glass is accompanied by a large dielectric relaxation strength (dielectric loss and static dielectric constant). This larger dielectric relaxation st rength of mixed alkali glasses compared with the corresponding single alkali glasses appears due to a negative enthalpy of mixing of two dis similar alkali species. This fact has been experimentally confirmed. C orrespondingly, the activity coefficient of one alkali component decre ases drastically by the addition of a second alkali component and this behavior appears to be analogous to the pronounced decrease of a trac er diffusion coefficient when a second alkali component is added. The thermodynamic state of glasses is controlled, primarily, by the charge interactions. The apparent correlation between the thermodynamics and the transport phenomena, as well as other features of the mixed alkal i effect, such as the diminishing mixed alkali effect in a high electr ic field, can be explained, at least qualitatively, using the electrol yte theory based upon the Coulombic interactions of charged species or iginally developed by Debye and Huckel.