High-temperature behavior of CsH2PO4 under both ambient and high pressure conditions

Dane A. Boysen, Sossina M. Haile*, Hongjian Liu, Richard A. Secco

*Corresponding author for this work

Research output: Contribution to journalArticle

148 Scopus citations

Abstract

The high-temperature behavior of CsH2PO4 has been carefully examined under both ambient and high pressure (1.0 ± 0.2 GPa) conditions. Ambient pressure experiments encompassed thermal analysis, AC impedance spectroscopy, 1H NMR spectroscopy, and polarized light microscopy. Simultaneous thermogravimetric analysis, differential scanning calorimetry, and evolved gas analysis by mass spectroscopy demonstrated that a structural transition with an enthalpy of 49.0 ± 2.5 J/g occurred at 228 ± 2 °C, just prior to thermal decomposition. The details of the decomposition pathway were highly dependent on sample surface area, however the structural transformation, a superprotonic transition, was not. Polarized light microscopy showed the high temperature phase to be optically isotropic in nature, consistent with earlier suggestions that this phase is cubic. The conductivity of CsH2-PO4, as revealed by the impedance measurements, exhibited a sharp increase at the transition temperature, from 1.2 × 10-5 to 9.0 × 10-3 Ω1-cm-1, followed by a rapid decline due to dehydration. In addition, chemically adsorbed surface water was shown to increase the conductivity of polycrystalline CsH2PO4 over well-dried samples, even at mildly elevated temperatures (>200 °C). At high pressure an apparent irreversible phase transition at 150 °C and a reversible superprotonic phase transition at 260 °C were observed by impedance spectroscopy. At the superprotonic transition, the conductivity increased sharply by ∼3 orders of magnitude to 3.5 × 10-2 Ω1-cm-1 at 275 °C. This high conductivity phase was stable to the highest temperature examined, 375 °C, and exhibited reproducible and highly Arrhenius conduction behavior, with an activation energy for charge transport of 0.35 eV. Upon cooling, CsH2PO4 remained in the high-temperature phase to a temperature of 240 °C.

Original languageEnglish (US)
Pages (from-to)727-736
Number of pages10
JournalChemistry of Materials
Volume15
Issue number3
DOIs
StatePublished - Feb 11 2003

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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