Theoretical Observation on The Experimental Data of Ge-Se-Tl System

Abstract

Understanding of the effect of addition Tl on glassy Ge-Se have been experimentally and theoretically investigated. The correlation between the optical gap opt Eg , the activation energy ∆Eσ , the pre-exponential factor σ o and theoretical calculations has greatly improved with the advent of several structural and chemical models which predict the influence of such an addition, in terms of the average number of constrains Ncon , the effective average coordination number < reff >, the average heat of atomization Hs , the glass forming ability and the number of Lone-pair (LP) electrons. The decrease in ∆Eσ and σ o with increasing Tl content has been discussed on the basis of structural changes in Ge-Se which leads to a readjustment in the local enviroment. Thallium is supposed to form states different from the valence states of elements interacting with Ge-Se according to the octet rule (8-N). A correlation has been found between the Ge-Se-Tl glassy system and the number of LP electrons. The stable vitreous state can be obtained only if enough lone-pair electrons exist in the structure of the glassy system. A simple criterion for computing the ability of a semiconductor system to retain its vitreous state is proposed. Investigation of the experimental data of the Ge-Se-Tl glassy system revealed that Ncon and < reff > has a strong effect on these properties and this supports the above analysis.