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Finite-Temperature Behavior of PdHx Elastic Constants Computed by Direct Molecular Dynamics

Published online by Cambridge University Press:  30 May 2017

X. W. Zhou*
Affiliation:
Sandia National Laboratories, 7011 East Avenue, Livermore, CA 94550, U.S.A
T. W. Heo
Affiliation:
Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, U.S.A.
B. C. Wood
Affiliation:
Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, U.S.A.
V. Stavila
Affiliation:
Sandia National Laboratories, 7011 East Avenue, Livermore, CA 94550, U.S.A
S. Kang
Affiliation:
Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, U.S.A.
M. D. Allendorf
Affiliation:
Sandia National Laboratories, 7011 East Avenue, Livermore, CA 94550, U.S.A
*
*(Email: xzhou@sandia.gov)
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Abstract

Robust time-averaged molecular dynamics has been developed to calculate finite-temperature elastic constants of a single crystal. We find that when the averaging time exceeds a certain threshold, the statistical errors in the calculated elastic constants become very small. We applied this method to compare the elastic constants of Pd and PdH0.6 at representative low (10 K) and high (500 K) temperatures. The values predicted for Pd match reasonably well with ultrasonic experimental data at both temperatures. In contrast, the predicted elastic constants for PdH0.6 only match well with ultrasonic data at 10 K; whereas, at 500 K, the predicted values are significantly lower. We hypothesize that at 500 K, the facile hydrogen diffusion in PdH0.6 alters the speed of sound, resulting in significantly reduced values of predicted elastic constants as compared to the ultrasonic experimental data. Literature mechanical testing experiments seem to support this hypothesis.

Type
Articles
Copyright
Copyright © Materials Research Society 2017 

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References

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