Solid-state chemistry of thallous tungstates

Abstract

The reaction between thallous carbonate and tungstic oxide yielding thallous tungstate has been studied at 550 ± 10°C. Thallous tungstates of different colours are produced when it is heated at different temperatures for different periods and cooled at different rates. Analysis shows that all these species have the same molecular formula Tl₂WO₄. Identical X-ray diffraction patterns were obtained for white and coloured species. The crystal lattice of Tl₂WO₄ belongs to the hexagonal system with a=b=6.296 Å,, c=8.126 Å and Z=2. The pyknometric densities of the white and coloured species were found to be 7.95 ± 0.05 g/ml at 30 ± 0.1°C (the X-ray density is 7.85 g/ml). Absorptions at 600 mµ and 540 mμ have been observed in the reflectance spectra. All the species were diamagnetic. DTA and TGA measurements were made. The conductivity of thallous tungstates showed semiconducting behaviour in the temperature range 100-550°C.