Steady state movement of ion mixed-alkali glasses

It is emphasized that a solid glass exhibits the mixed-alkali effect in transport phenomena only when a vacancy mechanism prevails and three is a difference in the diameters of the dissimilar mobile ions. The vacancy is impeded by potential barriers attributed to the jump of a large ion into a small site. The sites of the ions are li nked by permeable gaps, the number of which around a site is usually two, rarely three or one. The linked sites form a three-dimensional network in which the the vacancy is confined to move. The network consists of open and blocked channels . A computer program was written to simulate the vacancy migration. The program obeys the consequences of the random walk theory. The inout data were the length of the channels, a parameter determining the probability for the impeded jump, and a weighting factor for the movement of the smaller ion at the network junction. The calculated values for the transport number of the ions, the conductivity and the diffusivity for the sodium ion agreefairly well with experiment for a sodium-potassium silicate glass system.