Density measurements of xRb(2)S+(1-x) B2S3 (0<=x<=0.75) glasses: Correlation with short range order

Densities of rubidium thioborate glasses, xRb(2)S + (1-x)B2S3, are reported over the range 0 less than or equal to x less than or equal to 0.75. The monotonic increase in the density with x out to 0.75 contrasts with the behavior of the lighter alkali thioborate glasses in which the density sharply maximizes at x similar to 0.2-0.35. The density increases from 1.7 g/ml for pure B2S3 to 2.69 g/ml at x = 0.75. The increase in density in the region 0 less than or equal to x less than or equal to 0.3 arises from the increasing fraction of the heavier, but only slightly larger volume, tetrahedral boron group (Rb+BS2-) formed in these glasses by the addition of Rb2S to B2S3. The further density increase in the region 0.3 less than or equal to x less than or equal to 0.75 is associated with the increasing fractions of the metathioborate groups (B3S63-) and orthothioborate groups (BS33-) with terminal and heavy rubidium ions. The molar volumes of short range order groups were estimated by fitting the density data based upon the B-11 nuclear magnetic resonance and infrared spectra of these glasses. The calculated densities were in good agreement with the experimental data.