Synthesis, structure, and properties of compounds in the NaHSO₄-CsHSO₄ system. 2. The absence of superprotonic transitions in Cs₂Na(HSO₄)₃ and CsNa₂(HSO₄)₃

Exploratory synthesis in the NaHSO₄-CsHSO₄ system, aimed at discovering novel protonconducting solids, yielded the new compounds CsNa₂(HSO₄)₃ and Cs₂Na(HSO₄)₃. Thermal analysis demonstrated the absence of phase transitions for both compounds prior to melting. The conductivities of the two compounds vary monotonically with temperature, in a nonArrhenius manner, from ambient to the respective melt temperatures of 398 and 413 K. At 363 K the conductivities are on the order of 10^-8 Ω^1-cm^-1, which is comparable to that of other alkali acid sulfates. The absence of transitions to disordered, high conductivity phases, as is observed in compounds such as CsHSO₄, is explained in terms of the stiffness of the Na-O bonds, which may serve to prevent rapid reorientation of SO₄ tetrahedral groups.