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Analysis of glass forming ability using percolation concept and tunability of physical parameters of a-Ge12Se76 – xAs12Bix glassy semiconductors

Sharma I., Sunder S.

Materials Science Poland

2018

Vol. 36, No. 2

242--254

Glass forming ability of lone-pair semiconductors was analyzed for (x = 0, 2, 4, 6, 8, 10) system. Values of lone pair electrons L were calculated using average coordination number of valence electrons. These values were found to decrease, as the system was moving towards the rigid region. L > 3 values showed vitreous state. Deviation of the stoichiometry confirmed the chalcogen-rich region. A linear correlation was found between the mean bond energy and glass transition temperature. Chemical Bond Approach model was applied to calculate the cohesive energy of the system. A linear relationship was found to exist between the cohesive energy and the theoretical band gap, calculated using Shimakawa relation. A decrease in both parameters was explained on the basis of average stabilization energy and electronegativity of the system. The density values were found to increase and may account for higher refractive index of the system. Large Bohr radius of the Bi atom accounted for an increase in the polarizability. Other parameters viz. degree of covalency, packing density, compactness, molar volume, free volume percentage, excess volume and polaron radius were also calculated. An effort was made to correlate the effect of Bi addition to Ge12Se76 – xAs12Bix lone-pair semiconductor on the basis of the structure of the glassy matrix or the connectedness of the material.

Theoretical prediction of physical parameters of Ge x Sb20−x Te80 (x = 11, 13, 15, 17, 19) bulk glassy alloys

Sharma I, Maheshwari M

Materials Science Poland

2014

Vol. 32, No. 4

661--668

Physical properties of GexSb20−xTe80 (x = 11, 13, 15, 17, 19) bulk glassy alloys are examined theoretically. Lone pair electrons are calculated using an average coordination number (hri) and the number of valence electrons, and are found to decrease with an addition of Ge. Mean bond energy (hEi) is proportional to glass transition temperature (Tg) and shows maxima near the chemical threshold. Cohesive energy of the system is calculated using chemical bond approach. A linear relation is found between cohesive energy, band gap (calculated theoretically and confirmed experimentally) and average heat of atomization. All these parameters are increasing with an increase in Ge content. A relation between average single bond energy and photon energy is discussed. Compactness of the structure is measured from the calculated density of the glass. An attempt is made to discuss the results in terms of structure of the glass or equivalently with average coordination number.