Hydration, structure, and superconductivity of KOs₂O₆·nH₂O

Galati, R., Simon, C., Knee, C.S., Henry, P.F., Rainford, B.D. and Weller, M.T. (2008) Hydration, structure, and superconductivity of KOs₂O₆·nH₂O. Chemistry of Materials, 20 (4), 1652-1659. (doi:10.1021/cm702972c).

Abstract

In moist air or by contact with water during washing, KOs₂O₆ absorbs water molecules into the structure to produce KOs₂O₆·nH₂O, 0 < n < 0.1. This water is reversibly lost on heating above ~430 K in flowing or static gas environments. Variable temperature powder neutron and X-ray diffraction show that an increase in lattice parameter occurs when water enters the pyrochlore structure and the water molecules are located in the α cages displacing a portion of the potassium ions to adjacent sites. On removing water the lattice parameter and structure revert to those of the normal β-pyrochlore crystallographic description. Hydration has the effect of reducing the onset of superconducting behavior from a critical temperature of 10.25 K in fully dry KOs₂O₆ to 9.75 K in KOs₂O₆·0.1H₂O.

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