INFRARED-SPECTRA OF LITHIUM THIOBORATE GLASSES AND POLYCRYSTALS

Glasses and polycrystals in the xLi2S + (1-x)B2S3 system have been prepared over the composition range 0 less-than-or-equal-to xLi2S less-than-or-equal-to 0.80. The glass-forming range was observed to be approximately 0.48 less-than-or-equal-to x less-than-or-equal-to 0.80 for liquids splat-quenched from approximately 850-degrees-C into films approximately 0.25 mm in thickness. The infrared spectra of the glasses were interpreted as a progressive compositional shift from the glasses with x approximately 0.5 being based upon a mixture of trigonal (probably six-membered rings) and a high fraction tetrahedral boron groups to glasses with x approximately 0.80 being based upon isolated trigonal orthothioborate anions. As with nearly all alkali borate and thioborate glasses in the high alkali region, x > 0.5, a decreasing fraction of tetrahedral borons is observed. The fraction of tetrahedral borons for glasses with x approximately 0.55 is very large, but diminishes to zero for glasses with x = 0.75 and 0.80. Polycrystals were prepared at x = 0.33 (is similar to c-Li2B4S7), 0.5 (is similar to c-LiBS2) and 0.75 (c-Li3BS3). For the first two phases, all borons were found to be tetrahedrally coordinated, whereas for the last phase all borons were found to be in trigonal coordination.