E0075

Amorphous/Amorphous Phase Transitions in Two Componenent Melts. Cornelius T. Moynihan, Materials Science and Engineering Dept., Rensselaer Polytechnic Institute, Troy, NY 12180, USA

An apparent first order amorphous/amorphous (a/a) phase transition not accompanied by a composition change has been observed by Aasland and McMillan in Al2O3-Y2O3 melts. At first glance this observation appears to be anomalous, since the absence of a composition difference betwen two phases in a two component system is not allowed by thermodynamics if the two phases are in equilibrium. Extension of the two species/nonideal solution model for a/a transitions [1] to a two component system, however, shows that an a/a transition of the type observed in the Al2O3-Y2O3 melts is thermodynamically possible if it occurs under conditions where one of the amorphous phases is metastable.

[1] C. T. Moynihan, Mat. Res. Soc. Symp. Proc., 455, 411 (1997).