Tl 2SO 4–Li 2SO 4 phase diagram and properties of TlLiSO 4

Abstract

Using classical methods, differential thermal analysis (DTA) and X-ray powder diffraction at different temperatures, the Tl 2SO 4–Li 2SO 4 phase diagram has been re-examined. Several changes were observed from a previous study. Two small domains of primary solid solution with β-Li 2SO 4 (low-temperature form) and α-Tl 2SO 4 (high-temperature form) structures have been found, along with the β 2-Tl 2SO 4↔α–Tl 2SO 4 transition. The mixed sulfate TlLiSO 4 exists under two forms. The low-temperature form β is orthorhombic with a=8.3815(4) Å, b=9.2914(4) Å and c=5.3175(3) Å; the space group is Pnam or Pna2 1 with Z=4. The high-temperature form α is hexagonal with a=18.6699(8) Å and c=8.7015(6) Å; the space group is P6 3 with Z=24. The X-ray powder patterns are given. The structures of these two varieties belong to the stuffed-tridymite type. The β↔α transition occurs at 531°C with a modification of the structural skeleton topology and an increase (×120) of the electrical conductivity which leads to classify TlLiSO 4 as a superionic conductor.