Phase Transition and Crystal Structure of CsHSeO4 and CsDSeO4 Crystals

Takanori Fukami,Keiko Nakasone,Shuta Tahara,Mitsuhiro Seino

doi:10.5539/ijc.v5n3p1

Abstract

DSC, TG-DTA and X-ray diffraction measurements have been performed on cesium hydrogen selenate CsHSeO 4 and deuterated CsDSeO 4 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 P 2 1 / 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) A. The geometric isotope effect on the hydrogen bond structure by deuteration was realized in the CsHSeO 4 crystal. The experimental results denied the existence of a phase transition from phase II to III in the proton and deuterated compounds.

Highlights

Alkali ions (M+ = K+, Rb+, Cs+, or Na3H(SO4)2 and (NH4)+) and sulfate ions (XO42, where X = S or Se) exist generally in five types of compounds with the following chemical formulas: M2XO4, MHXO4, M3H(XO4)2, M5H3(XO4)4, and M3H5(XO4)4
We summarize the results from Differential scanning calorimetry (DSC), thermogravimetric-differential thermal analysis (TG-DTA) and X-ray diffraction measurements for CsHSeO4 and CsDSeO4 crystals
It is found that the thermal decomposition for both compounds starts at around the transition temperature, and the maximum rate of weight loss takes place at around 490 K

Summary

Introduction

Cesium hydrogen selenate (CsHSeO4) crystal belongs to a family of MHXO4-type compounds, and undergoes two phase transitions at TI-II (401 K) and TII-III (323-370 K) with three phases (Baranov et al, 1982, 1984; Checa et al, 2009; Colomban et al, 1986; Kamazawa et al, 2010; Komukae et al, 1990; Luspin et al, 1995, 2000; Ortiz et al, 2008; Pham-Thi et al, 1985; Yokota, 1982; Yokota et al, 1982). The structure in phase I has been reported to be tetragonal with space group I41/amd (Foose & Mitra, 1977; Komukae et al, 1990; Yokota, 1982)

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