ASIAN JOURNAL OF PHYSICS

Asian Journal of Physics                                                                                                          Vol. 9, No 3 (2000) 709-721

The Maximum in Glass Transition Temperature (T_g) near x = 1/3 in Ge_xSe_1-x Glasses

PP BOOLCHAND

Department of Electrical, Computer Engineering and Computer Science,
University of Cincinnati, Cincinnati, OH 45221-0030, USA

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We review results of Raman scattering, Mössbauer spectroscopy and T-modulated Differential Scanning Calorimetry experiments on Ge_xSe_1-x glasses. The molecular origin of the maximum in T_g near x=1/3 or mean coordination r- =2(1+x)=2.67. suggested by these experiments, implies that a nanoscale phase separation of the glass network takes place into Se-rich (A) and Ge-rich (B) molecular clusters. Phase separation on a molecular scale initiates at x > 0.31, and the B phase becomes the dominant one for x >0.35. In particular, in contrast to α - and β -  crystalline GeSe2, stoichiometric GeSe₂ glass is neither chemically ordered nor a continuous network. In ternary Ge_xAs_ySe_1-x-y, glasses at x=y, such nanoscale phase separation is apparently suppressed by chemical alloying As for r- up to 3.0. and T_gs are found to increase continuously with r-