Structural and vibrational characteristics of Ge-S-Br glass system: ab initio calculation and Raman study

To improve the understanding of the structure network of chalcogenide glass, we report an investigation of the structure and vibrational property of the Ge-S-Br system chalcogenide glass. The structural origin was interpreted by the result of ab initio calculation performed on the basic units such as ethane-like(ETH) structure(Ge2S6 and Ge2Br6),edge-sharing(ES) structure Ge2S2SnBr4-n (n=0,1,2,3,4) and isolated GeSnBr4-n tetrahedron (n=0,1,2,3,4), which represent the local structure of Ge-S-Br glassy system. In addition, We have compared the experimental spectra of GeS2, GeS3Br, GeSBr2 glasses and liquid GeBr4 to the calculated main vibrational modes of basic units by ab initio calculation. The calculated vibrational modes of the GeSnBr4-n cluster are assigned by group theory. Moreover, the symmetrical stretching modes related to the Ge-S and Ge-Br bond are in accordance with the vibrational coupling theory. The variation of calculated main vibrational modes of GeSmBrn clusters reveals the structure formations of Ge-S-Br glassy system with different S/Br ratios, which can be in agreement with vibrational spectra of Ge-S-Br glass.