Abstract

DSC, TG-DTA and X-ray diffraction measurements have been performed on cesium hydrogen selenate CsHSeO₄ and deuterated CsDSeO₄ crystals. The superionic phase transitions for the proton and deuterated compounds were found to occur at 402.6 and 398.1 K, respectively. The thermal decomposition accompanied by hydrolysis in both compounds started at around the transition temperature, and the maximum rate of weight loss from the reaction was observed at around 490 K. The space group symmetry (monoclinic P2₁/c) and structural parameters were determined at 298 and 355 K. The expansion of the O-H-O hydrogen bond at room temperature by the substitution of deuterium for hydrogen was observed to be 0.015(7) Å. The geometric isotope effect on the hydrogen bond structure by deuteration was realized in the CsHSeO₄ crystal. The experimental results denied the existence of a phase transition from phase II to III in the proton and deuterated compounds.

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