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High-temperature behavior of CsH_2PO_4 under both ambient and high pressure conditions

Boysen, Dane A. and Haile, Sossina M. and Liu, Hongjian and Secco, Richard A. (2003) High-temperature behavior of CsH_2PO_4 under both ambient and high pressure conditions. Chemistry of Materials, 15 (3). pp. 727-736. ISSN 0897-4756. doi:10.1021/cm020138b.

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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 CsH₂PO₄, 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.

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Haile, Sossina M.0000-0002-5293-6252
Alternate Title:High-temperature behavior of CsH2PO4 under both ambient and high pressure conditions
Additional Information:Copyright © 2003 American Chemical Society. Received October 4, 2002. Publication Date (Web): January 17, 2003. CM020138B. This work was supported by a grant from the U.S. National Science Foundation. We thank Dr. Sonjong Hwang at Caltech’s Solid State NMR Facility for assistance with NMR measurements.
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Subject Keywords:phase-transitions conductivity crystals
Issue or Number:3
Record Number:CaltechAUTHORS:20131125-162530229
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Official Citation:High-Temperature Behavior of CsH2PO4 under Both Ambient and High Pressure Conditions. Dane A. Boysenand, Sossina M. Haile*, Hongjian Liu and, and Richard A. Secco. Chemistry of Materials 2003 15 (3), 727-736.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42703
Deposited By: Jonathan Gross
Deposited On:27 Nov 2013 19:33
Last Modified:10 Nov 2021 16:27

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