Correlation between the physical and optical properties of the a-Ge–Se–In–Bi system

Abstract

A correlation between physical and optical properties of the Ge₂₀Se_{70− x} In₁₀Bi _x (x = 0, 2, 4, 6, 8, 10) glassy system is presented. The density of the alloys increases with an increase of the Bi content, which accounts for the concurrent increase in refractive index. The molar volume (V_m ) has been calculated from the densities and follows the same trend as that of the optical gap. A linear relation has been found between the cohesive energy (calculated using a chemical-bond approach) and the optical gap (experimental and theoretical). The cohesive energy and the optical gap decrease with increase in Bi content. A decrease of electronegativity also accompanies the decrease of optical gap. The relationship between the optical gap and the chemical composition in the a-Ge–Se–In–Bi glasses has been examined using two parameters: the average heat of atomization and the average coordination number (⟨r⟩). The mean bond energy (⟨E⟩) and the glass transition temperature (T_g ) are calculated using the Tichy-Ticha approach. ⟨E⟩ shows maxima at chemical thresholds. Thickness-dependence studies of the optical gap and the refractive index show that optical gap increases with increased thickness, whereas no significant change has been found in the refractive index for all compositions.

Keywords:

• chalcogenide glasses
• cohesive energy
• glass transition temperature
• optical properties