Structure and Vibrational Spectrum of β-Cs_3(HSO_4)_2[H_(2−x)(P_(1−x), S_x)O_4] (x∼0.5), a New Superprotonic Conductor, and a Comparison with α-Cs_3(HSO_4)_2(H_2PO_4)

Abstract

The structure of the new protonic conductor, β-Cs₃(HSO₄)₂(H₂₋ₓ(P₁₋ₓ, Sx)O₄) (with a superprotonic transition at 125°C), has been determined by single-crystal X-ray diffraction methods. Structural features of this and the related compound,α-Cs₃(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)Å, and β=100.11(2)° and a unit cell volume of 1387.5(14)ų, implying a density of 3.304 g/cm³. 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(F²)=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 α-Cs₃(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 β-Cs₃(HSO₄)₂(H₂₋ₓ(P₁₋ₓSₓ)O₄) support the assumption of greater structural disorder in this compound than in α-Cs₃(HSO₄)₂(H₂PO₄).

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