Mixed‐Alkali Effect and Interdiffusion of Na and K Ions in Glass

When 2 alkali ions are present in a glass, its electrical conductivity is reduced compared to that of glasses containing only one of these ions. Measurements of electrical mobility and tracer diffusion show that the mobilities of individual ions are reduced by the presence of a second ion. Thus, theories have been proposed to explain the mixed‐alkali effect in terms of ionic interactions. However, experiments on interdiffusion of Na and Ag or K ions in soda‐lime glass indicate that at sufficiently low temperatures the mobilities of the interdiffusing ions are not influenced by the presence of the second ion. Therefore, it is postulated that structural rearrangement of the glass is required for the mixed‐alkali effect.