Glass formation, properties, and structure of the glasses based on GeS2-Sb2S3-CsX (X=Cl, Br, I)

Glass formation and properties were systematically investigated for the ternary chalcohalide systems, GeS2-Sb2S3-CsX (X=Cl, Br, I). Caesium halides were incorporated into the binary GeS2-Sb2S3 glasses through the replacement of GeS2 or Sb2S3. Glasses were obtained for the replacement levels up to 25 mol% (X=Cl and Br) or 30 mol% (X=I) of CsX. For the case in which GeS2 in 60GeS(2.)40SbS(3/2) glass was replaced by CsX, the glass transition temperatures monotonically decreased from 319 degrees C to 230-240 degrees C with increasing CsX content while the densities of the glasses increased. On the other hand, the dependences of the refractive indices on the CsX content were not simple; they slightly increased from 2.39 at 633 nm for the initial replacement of GeS2 by CsX up to 5 to 10 mol% and then, decreased with increasing CsX content, finally reaching about 2.3. This behaviour was discussed on the basis of the red-shift of the absorption edges on the short wavelength side with the initial replacement. Raman spectra were measured to determine the structural features of the glass network. The spectra were successfully decomposed into seven Gaussian curves assigned to the vibrational modes of structural units including GeS4 tetrahedra and SbS3 trigonal pyramids. The spectra hardly varied with the replacement GeS2 by CsX or with the halogen type. Finally, the crystallization behaviours were investigated for the glasses with the compositions near the border of the glass forming regions through two-step heat treatments. The CsX or GeS2 crystallites precipitated from the glasses contained large amounts of CsX or GeS2, respectively.