The electronic and structural changes in the supercooled liquid and glassyAs2Se3

We have measured extended X-ray absorption fine structure (EXAFS) and de co nductivity sigma of the liquid and glassy As2Se3. Each \F(r)\, the magnitud e of the Fourier transform of EXAFS oscillations around As and Se atoms, ha s a symmetric peak around 2.5 Angstrom. The curve fitting analysis indicate s the presence of chemical order and no homopolar As-As and Se-Se bonds. Wh en liquid As2Se3 is cooled to the glassy state through the supercooled stat e, the inter-layer correlation increases and the two-dimensional (2D) As2Se 3 network structure transforms to a three-dimensional (3D) one. This transf ormation is the reason for the change in the temperature variation of the c oordination number N around 300 degrees C whose temperature is higher than T-g(= 181 degrees C). The change in the slope of log sigma versus 1/T aroun d 300 degrees C is assumed to be associated with the appearance of broadene d and localized charged defect states near the band tail. (C) 1999 Elsevier Science B.V. All rights reserved.