DENSITY-DRIVEN LIQUID-LIQUID PHASE-SEPARATION IN THE SYSTEM AL2O3-Y2O3

Phase separation of liquid mixtures into two liquids with different co mpositions is a well-known phenomenon. It has been proposed(1-9) that another type of liquid-liquid phase separation, driven by fluctuations in density rather than in composition, may occur in some elemental sy stems. Transitions between low- and high-density amorphous phases have been described for the one-component oxides H2O, SiO2 and GeO2 (refs 10-17), and it has been suggested(18-21) that a liquid-liquid phase tr ansition might occur in supercooled water. If density-driven phase sep aration truly does occur in liquid mixtures, it should be possible to observe the coexistence of two liquids with the same composition but d ifferent density. Here we report the direct observation of such a situ ation. We observe two coexisting liquid phases in the supercooled melt of Al2O3-Y2O3 just above the glass transition at ambient pressure, bo th of which have the same composition. We propose that these two phase s must differ solely in density, and that the transition is entropical ly driven. The occurrence of the phase transition in this system may e xplain why the crystallization of yttrium aluminium garnet, the host m aterial for Nd3+ ions in YAG lasers, is sluggish(22-25).