Molar Volumes in Molten NaBr, RbBr, NaBr-TlBr and RbBr-TlBr

Abstract

Densities in molten NaBr and RbBr and molar volumes in their binary mixtures with TlBr are reported. The pyknometric method again gave slightly higher densities (0.1 - 0.2%) than previous Archimedean methods. In the mixtures the excess volume is no greater than ±1% but its variation with composition and temperature broadly resembles that in the MX-TIX systems reported previously. A relationship is apparent between the overall trend in the molar volume with composition and temperature and the variation in the Tl-X overlap by nmr. Together with the stoichiometry, this suggests that in the region of strong negative deviation coordination is high and localized orbital overlap low between cations and anions.