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

The IR spectra of xCs2S+(1−x)B2S3 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-Cs2S:2B2S3 (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-Rb2S:2B2S3. The Li, Na, and K dithioborate phases, however, consist solely of tetrahedral borons. The IR spectrum of c-Cs2S:B2S3, the meta-thioborate phase (x=0.50), shows that this phase consists of four-membered ring meta-thioborate groups, Cs2B2S4, with two non-bridging and two bridging sulfurs. Contrasting this behavior, the IR spectra of c-M2S:B2S3, with M=Na, K and Rb, shows that these phases are solely comprised of six-membered ring meta-thioborate groups, M3B3S6. For the polycrystal with x=0.75, c-Cs3BS3, the IR spectrum indicates that this phase consists of trigonal ortho-thioborate groups, Cs3BS3, similar to those of the Li, Na, K, and Rb phases. The IR spectra of glassy B2S3 has been shown by previous work to consist of equal fractions of isolated `looseʹ trigonal groups and six-membered thioboroxyl ring groups. With the addition of Cs2S to B2S3 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.