STRUCTURE OF CS-3(HSO4)(2)(H2PO4) - A NEW COMPOUND WITH A SUPERPROTONIC PHASE-TRANSITION

Solid-solution studies in the CsHSO4-CsH2PO4 system carried out in a s earch for low-temperature proton conducting materials yielded the new compound Cs-3(HSO4)(2)(H2PO4) [tricesium bis(hydrogensulfate) dihydrog enphosphate]. Single-crystal X-ray measurements (performed at room tem perature) revealed that Cs-3(HSO4)(2)(H2PO4) crystallizes in space gro up P2(1)/n and has lattice parameters a = 19.546(3), b = 7.8798(10), c = 9.1854(17)Angstrom and beta = 100.536(14)degrees. With four formula units in the unit cell, and a cell volume of 1390.7(4)Angstrom(3), Cs -3(HSO4)(2)(H2PO4) has a calculated density of 3.295 Mg m(-3). 18 non- H atoms were located in the asymmetric unit. Refinement using anisotro pic temperature factors for all 18 non-H atoms