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Conductivity of potassium and rubidium dihydrogen phosphates at high temperature and pressure

Boysen, Dane A. and Haile, Sossina M. and Liu, Hongjian and Secco, Richard A. (2004) Conductivity of potassium and rubidium dihydrogen phosphates at high temperature and pressure. Chemistry of Materials, 16 (4). pp. 693-697. ISSN 0897-4756. doi:10.1021/cm034954a.

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The high-temperature behavior of KH₂PO₄ and RbH₂PO₄ has been investigated by several methods. Simultaneous differential scanning calorimetry and thermal gravimetry, combined with evolved gas analysis, was carried out from 25 to 500 °C under ambient pressure. The initial dehydration events in KH₂PO₄ and RbH₂PO₄ occur at 233 and 257 °C, respectively, with no indication of either solid−solid or solid−liquid transitions prior to weight loss. Application of pressure suppresses this dehydration. Impedance spectroscopy performed under 1 GPa revealed a highly reproducible superprotonic phase transition in RbH₂PO₄ at 327 °C, at which the conductivity increased several orders of magnitude to a value of 6.8 × 10⁻² Ω⁻¹ cm⁻¹ at 340 °C. The activation energy for proton transport in the superprotonic phase is ΔHₐ of 0.232 ± 0.008 eV and the pre-exponential factor A, 3.4 ± 0.6 × 10³ Ω⁻¹ cm⁻¹ K. No superprotonic solid−solid phase transition was observed in KH₂PO₄. However, a sharp increase in conductivity to a value of 1.8 × 10⁻² Ω⁻¹ cm⁻¹ at 345 °C was observed upon melting (Tm ∼ 325 °C). The liquid phase exhibited Arrhenius behavior comparable to that of superprotonic RbH₂PO₄, with ΔHₐ= 0.227 ± 0.004 eV and A = 5. 2 ± 0.5 × 10³ Ω⁻¹ cm⁻¹ K.

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Haile, Sossina M.0000-0002-5293-6252
Additional Information:Copyright © 2004 American Chemical Society. Received October 5, 2003. Revised Manuscript Received November 26, 2003. Publication Date (Web): January 30, 2004. CM034954A. Funding for this work has been provided by the National Science Foundation, Division of Materials Research.
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Subject Keywords:phase-transitions csh2po4 rbh2po4 crystals kh2po4 family form ion
Issue or Number:4
Record Number:CaltechAUTHORS:20131125-162530354
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Official Citation:Conductivity of Potassium and Rubidium Dihydrogen Phosphates at High Temperature and Pressure. Dane A. Boysen and, Sossina M. Haile*, Hongjian Liu and, and Richard A. Secco. Chemistry of Materials 2004 16 (4), 693-697.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42704
Deposited By: Jonathan Gross
Deposited On:27 Nov 2013 19:17
Last Modified:10 Nov 2021 16:27

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