Stable and metastable phase equilibria in the GeSe2-Se system

Stable and metastable phase equilibria in the binary system GeSe2-Se have b een investigated by means of optical and electron microscopy, electron prob e microanalysis (EPMA), x-ray diffraction (XRD), thermal analysis, and adia batic calorimetry. A revised equilibrium phase diagram is presented, A not previously observed lambda-type phase transition was observed near similar to 420 K (147 degrees C) for GeSe2, The intermediate phase, phi, which earl ier had been considered as metastable, is shown to be stable through extens ive annealing experiments and by adiabatic calorimetry, The phi phase, with composition near Ge3Se7, melts incongruently at 658 +/- 5 K (385 +/- 5 deg rees C) to GeSe2 and a liquid with 85 +/- 2 at.% Se, The liquidus of GeSe2 and phi was determined by EPMA of annealed-and-quenched samples. Both a sta ble (phi-Se-liquid) and a metastable (GeSe2-Se-liquid) eutectic point were observed. The stable one was observed at 480 +/- 2 K (207 +/- 2 degrees C) and 92.5 +/- 1.0 at. % Se, whereas the temperature of the metastable eutect ic (GeSe2-Se-liquid) was observed to be similar to 10 K lower. Metastable p hase equilibria, obtained on thermal evolution of glasses with different co mpositions, are described and discussed.