Optical and calorimetric studies of Ge-Sb-Se glasses

Optical properties of amorphous GexSb40-xSe60 (x = 22.5, 25, 27.5, 30 and 3 2.5 at.%) thin films prepared by electron beam evaporation have been measur ed in the visible and near-infrared spectral region. The variations of the electronic energy gap (E-g) with composition are discussed on the basis of both the overall mean bond energy and the topological model based on the st ructural dimensionality considerations. A pronounced peculiarity (maximum o r minimum) appeared at around the same value of the average coordination nu mber (Z) = 2.65 for all the compositional dependencies of electronic energy gap, high frequency dielectric constant, optical relaxation time and the d ispersion parameters, is attributed to a topological phase transition from two-dimensional (2D) layer type to three-dimensional (3D) crosslinked netwo rk structures in the present glassy thin films. This confirms the suitabili ty of structural topological model to explain the compositional dependencie s of the physical parameters, not only for bulk glasses but also for thin f ilms evaporated from them. These results are supported by volumetric and th e calorimetric measurements. (C) 2000 Elsevier Science B.V. All rights rese rved.