No abstract

Sodium Thiosulphate, Polymorphism, Solid ElectrolyteNa2S2C>3 crystallizes in 4 modifications. The familiar monoclinic a-form stable at ambient temperature transforms into the trigonal /3-form at 330 °C which at 388 °C converts to bcc y-Na2S203. These transformations are reversible. Unstable orthorhombic a'-Na2S2C>3(Pna 2i) is obtained by dehydration of the pentahydrate or by cooling the ß-phase.The y-phase decomposes in sealed ampoule to Na2SC>4 and NaSs; decomposition is slow below and rapid above 440 °C. Equilibrium displacement by distillation of sulphur accelerates decomposition even for /?-Na2S203, and maintaining low sulphur pressure by pumping gives Na2S03. ß-and y-Na2S2C>3 are superionic conductors; a dynamic model is presented for the /3-structure with Na+ conduction pathways originating from oscillation of the S0O3 2-tetrahedra. Structural relationships can be derived with respect to the arrangement of the thiosulphate groups.