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Evidence for a Structural Transition to a Superprotonic CsH2PO4 Phase Under High Pressure

Published online by Cambridge University Press:  01 February 2011

Cristian E. Botez
Affiliation:
[email protected], University of Texas at El Paso, Physics, 500 W. University Ave., El Paso, Texas, 79968, United States, 915-747-8040, 915-747-5447
Russell R. Chianelli
Affiliation:
[email protected], University of Texas at El Paso, Department of Chemistry and Materials Research Institute, El Paso, Texas, 79968, United States
Jianzhong Zhang
Affiliation:
[email protected], Los Alamos National Laboratory, Los Alamos Neutron Scattering Center, Los Alamos, New Mexico, 87545, United States
Jiang Qian
Affiliation:
[email protected], Los Alamos National Laboratory, Los Alamos Neutron Scattering Center, Los Alamos, New Mexico, 87545, United States
Yusheng Zhao
Affiliation:
[email protected], Los Alamos National Laboratory, Los Alamos Neutron Scattering Center, Los Alamos, New Mexico, 87545, United States
Juraj Majzlan
Affiliation:
[email protected], University of Freiburg, Institute of Mineralogy and Geochemistry, Freiburg, N/A, 79104, Germany
Cristian Pantea
Affiliation:
[email protected], Los Alamos National Laboratory, Materials Science and Technology - National High Magnetic Field Laboratory, Los Alamos, New Mexico, 87545, United States
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Abstract

We have used synchrotron X-ray powder diffraction (SXRPD) to investigate the structural behavior of cesium dihydrogen phosphate upon heating. Temperature-resolved data collected at ambient-pressure demonstrate that a transition from the room-temperature monoclinic phase (P21/m; a=7.90Å, b=6.39Å, c=4.87Å, and β=107.64°) to a high-temperature cubic phase (Pm3m; a=4.96Å) occurs at T=237°C. The high-temperature phase is not stable under ambient-pressure conditions, even in the absence of further heating. On the other hand, SXRPD measurements carried out under high-pressure (∼1GPa) evidence a transition from monoclinic to a stable cubic phase (Pm3m, a=4.88Å) at a temperature within the 255°C-275°C range. A 1000-fold increase in the proton conductivity (indicating the transition to the superprotonic phase) was previously observed under the same non-ambient conditions. Therefore, our results represent strong evidence that the superprotonic behavior in cesium dihydrogen phosphate is associated with a monoclinic-to-cubic polymorphic structural transition and not with chemical modifications.

Type
Research Article
Copyright
Copyright © Materials Research Society 2006

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