Models for the Phase Diagram of Palladium Hydride Including O-site and T-site Occupation
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JCMNS66.pdf
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Author(s)
Hagelstein, Peter L
Date Issued
2016
Journal
Journal of Condensed Matter Nuclear Science
Publisher
International Society of Condensed Matter Nuclear Scientists (ISCMNS)
Citation
Hagelstein, Peter L. "Models for the Phase Diagram of Palladium Hydride Including O-site and T-site Occupation." Journal of Condensed Matter Nuclear Science 20 (2016): 54-80 © 2016 ISCMNS
Version
Final published version
Abstract
Early statistical mechanics models for palladium hydride allowed for a good description of the phase diagram based on a simple parameterization of the O-site energy. In this work we study generalizations of these models to include higher-order dependence on loading, temperature-dependent O-site energies, and also to include T-site occupation. Experimental data sets for 10 isotherms were assembled, and augmented with additional extrapolated points for the low-pressure α-phase region as well as the high pressure β-phase region. Loading-dependent O-site energies are optimized by minimizing the mean square error in the chemical potential between the model and data set. The resulting models give a good match to the phase diagram. If the O-site energy is allowed to be temperature dependent then the fit is better, but the resulting optimum is a mathematical optimum not so closely connected with the physical system. Models were studied in which O-site and T-site occupation occurs. When optimized these models are able to provide a good match to the phase diagram. When the O-site to T-site excitation energy is fixed according to estimates developed in earlier studies, the resulting temperature-dependent O-site energies are physically plausible. When the excitation energy are optimized together with the O-site energy, the resulting optimum is a mathematical one much less connected to the physical system. An earlier analysis of solubility in the α-phase led to a strong argument that T-site occupation occurs in palladium hydride and in
palladium deuteriude; the present study supports this conclusion based on an independent data set. Keywords: Mean field model; Palladium hydride; Phase diagram; Statistical mechanics; T-site occupation
MIT Department
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
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DOI of Published Version
www.iscmns.org/CMNS/JCMNS-Vol20.pdf
