Electronic and structural changes in the supercooled liquid and glassy As₂Se₃

We have measured extended X-ray absorption fine structure (EXAFS) and dc conductivity σ of the liquid and glassy As₂Se₃. Each |F(r)|, the magnitude of the Fourier transform of EXAFS oscillations around As and Se atoms, has a symmetric peak around 2.5 angstroms. The curve fitting analysis indicates the presence of chemical order and no homopolar As-As and Se-Se bonds. When liquid As₂Se₃ is cooled to the glassy state through the supercooled state, the inter-layer correlation increases and the two-dimensional (2D) As₂Se₃ network structure transforms to a three-dimensional (3D) one. This transformation is the reason for the change in the temperature variation of the coordination number N around 300 °C whose temperature is higher than Tg( = 181 °C). The change in the slope of log σ versus 1/T around 300 °C is assumed to be associated with the appearance of broadened and localized charged defect states near the band tail.