COPPER AS AN ADDITIVE IN THE AS0.4SE0.3TE0.3 GLASS - MEAN ATOMIC VOLUME AND T-G

Data on the mean atomic volume (V) and the glass transition temperatur e (T-g) of the As0.4Se0.3Te0.3 glass, modified with Cu are reported an d discussed. The V and T-g of the parent glass are invariant with addi tion of less than or equal to 1 atomic percent (at.%) of Cu up to whic h clusters of Cu atoms occupy interlayer positions in the layered netw ork of the parent glass. For additions of Cu > I at.%, a decrease in V and an increase in T-g are observed. The composition dependencies of V and T-g are consistent with a model according to which, with progres sive increase in the Cu content, some of the original As2Se3 and As2Te 3 structural units of the parent glass are replaced, respectively, by CuAsSe2 and CuAsTe structural units. For Cu greater than or equal to 2 3.08 at.%, after the formation of CuAsSe2 structural units, there is n o free Se available for the formation of As2Se3 structural units; as n o free Se is available, a change of slope occurs in the V-composition and T-g-composition data at the Cu content of 23.08 at.%. The increase in T-g with increasing Cu content is due to an increase in the averag e coordination number brought about by an increase in cross linking du e to the formation of tetrahedral CuAsSe2 and CuAsTe complexes in the glasses. (C) 1997 Elsevier Science B.V.