Structure and vibrational spectrum of β-Cs3(HSO4)2[H2-x(P1-x, Sx)O4] (X∼0.5), a new superprotonic conductor, and a comparison with α-Cs3(HSO4)2(H2PO4)

The structure of the new protonic conductor, beta-Cs-3(HSO4)(2) (H1-x(P1-x, S-x)O-4) (with a superprotonic transition at 125 degrees C), has been determined by single-crystal X-ray diffraction methods. Structural features of this and the related compound, alpha-Cs-3(HSO4)(2)(H2PO4), have been further examined by Raman and IR spectroscopy. The new compound crystallizes in space group C2/c, contains four formula units in the unit cell, and has an x value (in the stoichiometry) of approximately 0.5, X-ray intensity data, collected at room temperature, yielded lattice parameters a=20.04(1), b=7.854(5), c=8.954(5)Angstrom: and beta= 100.11(2)degrees and a unit cell volume of 1387.5(14)Angstrom(3), implying a density of 3.304 g/cm(3). Within the asymmetric unit, 10 nonhydrogen atoms and 3 hydrogen sites were located. Refinement of the X-ray data using anisotropic temperature factors for all 10 of the former yielded residuals wR(F-2) = 0.0952 and R(F) = 0.0358. The structure contains alternating zig-zig chains of anion tetrahedra and cesium ions, in a manner similar to that found in alpha-Cs-3(HSO4)(2)(H2PO4) and in CsHSO4-II, The structure is unique, however, in that P and S occupy the same crystallographic position, and there is, accordingly, a variable H content and a partially occupied hydrogen bond. Broader peaks in the Raman spectrum of beta-Cs-3(HSO4)(2)(H2-x(P1-x,S-x)O-4) support the assumption of greater structural disorder in this compound than in alpha-Cs-3(HSO4)(2)(H2PO4). (C) 1998 Academic Press.