Infrared spectroscopy of glasses and polycrystals in the series xCs2S+(1−x)B2S3

The IR spectra of xCs ₂S+(1− x)B ₂S ₃ glasses and polycrystals are reported for the first time. Glasses can be continuously formed by quenching between two stainless steel plates out to x ∼0.60. Single-phase polycrystals appear to form at x=0.33, 0.50, and 0.75. The IR spectrum of c-Cs ₂S:2B ₂S ₃ ( x=0.33) shows that this phase consists of the dithioborate group having equal numbers of three- and four-co-ordinated borons similar to that of c-Rb ₂S:2B ₂S ₃. The Li, Na, and K dithioborate phases, however, consist solely of tetrahedral borons. The IR spectrum of c-Cs ₂S:B ₂S ₃, the meta-thioborate phase ( x=0.50), shows that this phase consists of four-membered ring meta-thioborate groups, Cs ₂B ₂S ₄, with two non-bridging and two bridging sulfurs. Contrasting this behavior, the IR spectra of c-M ₂S:B ₂S ₃, with M=Na, K and Rb, shows that these phases are solely comprised of six-membered ring meta-thioborate groups, M ₃B ₃S ₆. For the polycrystal with x=0.75, c-Cs ₃BS ₃, the IR spectrum indicates that this phase consists of trigonal ortho-thioborate groups, Cs ₃BS ₃, similar to those of the Li, Na, K, and Rb phases. The IR spectra of glassy B ₂S ₃ has been shown by previous work to consist of equal fractions of isolated `loose` trigonal groups and six-membered thioboroxyl ring groups. With the addition of Cs ₂S to B ₂S ₃ in the low-alkali region ( x<0.5) and similar to the behavior of the Na, K, and Rb thioborate glasses, the absorption band of the tetrahedral borons at ∼600–750 cm ⁻¹ reaches a maximum in intensity at x∼0.3. Tetrahedral borons appear to form initially from the loose trigonal groups, similar in behavior to the other alkali thioborate glasses. The IR glasses in the high-alkali region, x>0.5, resemble those of the other thioborate glasses where the fraction of the meta-thioborate groups decreases in preference to the formation of ortho-thioborate groups. Quite surprisingly, there is no IR spectral evidence of the formation of the four-membered ring Cs meta-thioborate groups in the glasses, even though this structure is observed in the polycrystals in this series.