INFRARED-SPECTROSCOPY OF GLASSES AND POLYCRYSTALS IN THE SERIES XK(2)S+(1-X)B2S3

The infrared (IR) spectra of binary xK(2)S + (1 - x)B2S3 glasses (0 less than or equal to x less than or equal to 0.75) and polycrystals of compounds are reported. Polycrystals were prepared at x = 0.33 (K2B4S7) x = 0.5 (KBS2), and x = 0.75 (K3BS3), and the IR spectra were found to be similar to those found in the corresponding sodium thioborate system. The boron local structure of the K2B4S7 phase was interpreted by comparison with the IR spectra of analogous Li and Na phases which have been observed to consist of groups in which all borons are tetrahedrally coordinated. The IR spectra of metathioborate phase (c-KBS2) was interpreted in terms of B3S6- rings. The IR spectra of the orthothioborate phase (c-K3BS3) indicates the formation of the highly charged and depolymerized orthothioborate unit (BS33-). For the glasses, the IR spectra indicate that, as K2S is added to B2S3, tetrahedral borons (BS4-) form in a manner similar to that in the sodium thioborate and alkali borate glasses. The band associated with the tetrahedral boron group increases in intensity up to xK(2)S similar or equal to 0.30, and decreases thereafter. For pure B2S3, the IR spectra is interpreted as arising from both isolated trigonal boron units and six-membered hexagonal rings. As the tetrahedral borons in these glasses form, they do so at the expense of the isolated trigonal boron groups with the thioboroxyl ring groups remaining largely unaffected. The frequency of the thioboroxyl ring mode, however, shifts systematically from similar to 1000 cm(-1) to 900 cm(-1) as x increases from 0 to 0.45, and becomes most pronounced at x similar or equal to 0.25, near to the composition where the intensity of tetrahedral boron group vibration maximizes. Beyond x = 0.35, the IR spectra show the formation of metathioborate groups and at x = 0.50, it is the dominant boron group present. At higher K2S contents (x greater than or equal to 0.60), the IR spectra show the subsequent progressive destruction of metathioborate groups, a decreasing the fraction of BS4- units, and an increasing fraction of depolymerized orthothioborate units.