Ceramics-Silikáty 58 (2) 95-98 (2014)

THERMODYNAMIC MODEL AND STRUCTURE OF As₂S₃–As₂Se₃ GLASSES BASED ON THE MCR ANALYSIS OF RAMAN SPECTRA

Raman spectra and structure of six glasses with the composition of xAs₂S₃∙(1 – x)As₂Se₃ (x = 1; 0.75; 0.667; 0.50; 0.25; 0) were studied. In our previous work the Raman spectral data were interpreted on the basis of the Shakhmatkin and Vedishcheva thermodynamic model, where the glass was treated as an ideal solution of five components, namely: As₂S₃, As₂Se₃, As₂S₂, AsSe, and Se. The lack of mixed S–Se compounds in the model does not allow the interpretation of the measured spectra taking into account the existence of mixed trigonal pyramids of the type As₂S_3-xSe_x. In the present work an alternative simple thermodynamic model was proposed based on two equilibrium reactions leading to formation of two types of mixed As₂S_3-xSe_x (x = 1, 2) pyramids. The results of multivariate curve resolution (MCR) analysis of the measured spectra were interpreted as proportional to the molar fractions of four system components: As₂S₃, As₂Se₃, As₂SSe₂, and As₂S₂Se. Using the nonlinear regression treatment the reaction Gibbs energies were optimized by minimization of the sum of squares of deviation between the MCR data and the equilibrium amounts of the systems components. The equilibrium system composition was calculated at experimentally determined glass transition temperature assuming the ideal behavior. It was found that the optimized values of reaction Gibbs energies fit the MCR data with acceptable accuracy.

Keywords: Glass structure, Thermodynamic model, Aarsenic trisulfide, Aarsenic triselenide