MIXED GLASS FORMER EFFECT IN THE SYSTEM 0.3LI(2)S-0.7[(1-X)SIS2-XGES(2)] - A STRUCTURAL EXPLANATION

A mixed glass former effect has been observed in the glassy system 0.3 Li(2)S-0.7[(1-x)SiS2-xGeS(2)], where 0 less than or equal to x less th an or equal to 1. It corresponds to a large enhancement of ionic condu ctivity for compositions 0.50 less than or equal to x less than or equ al to 0.64. The variations of the electrical characteristics are close ly related to those of the glass transition temperature and the densit y. Structural investigations by Raman and SAXS techniques have been ca rried out on this system. The results indicate that the high conductin g glasses belonging to the central composition region, i.e., 0.50 I x I 0.64, are phase separated, forming entities with a composition close to GeS2 which are embedded in a matrix close to Li2SiS3, while glasse s from the limiting composition ranges, i.e., 0 less than or equal to x < 0.50 and 0.64 < x less than or equal to 1, are homogeneous.