THEORETICALLY PREDICTED DEVIATION IN PHYSICAL PROPERTIES OF GE-BI-S CHALCOGENIDE ALLOYS WITH COMPOSITIONAL VARIATIONS

Abstract

Chalcogenide glasses (ChGs) semiconductors have several useful properties, especially in their technical applications. The present work explains the compositional dependence of many physical properties of Ge_xBi₅S_95-x (x = 0, 10, 20, 30, 35 and 45 at. %). Increasing Ge content reduces the fraction of floppy modes, the lone pair electrons, the stoichiometric deviation, and the heat of atomization, while the average coordination number 〈r〉, constraints, density, and molar volume increased, indicating the alloys have moved from floppy to rigid mode. The average overall bond energy, electronegativity difference, band gap energy, and glass transition temperature were estimated by analyzing the bond energies and its distribution based on the bond ordered network model (CONM). It has been found that all these parameters increase with Ge ≤ 30 at. % and decrease with the further increase of Ge content. This behavior can be explained in terms of the network chemical percolation threshold proposed by Tanaka. This threshold represents a topological phase transition from a two-dimensional structure at r˂2.67 to a three-dimensional structure at r≥2.67. The incorporation of Ge into the glassy Bi-S system yields interesting physical properties such as threshold and phase transition, confirming this composition's suitability for optical storage media.