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Title: Impact of anharmonicity on the vibrational entropy and specific heat of UO 2

Abstract

The impact of anharmonicity on the vibrational entropy and heat capacity of UO 2 has been discovered from 10 to 1200 K using inelastic neutron-scattering measurements of the phonon density of states (PDOS). Small changes in the PDOS are observed from 10 to 295 K, with more noticeable changes appearing in the 750- and 1200-K data. The specific heat determined from the PDOS measurements is in agreement with macroscopic specific heat measurements, and the overall impact of nondilation anharmonicity on the specific heat has been shown to be less than 2%. An analysis of the phonon measurements shows that the softening of acoustic phonons with temperature is consistent with the quasiharmonic approximation. The optical phonons deviate from the quasiharmonic prediction, with the low-energy optical phonons between approximately 20 and 50 meV softening more than expected, while the higher-energy optical phonons between approximately 50 and 80 meV have no appreciable softening over the temperature range measured. The observation of a small anharmonic specific heat contribution has been demonstrated to be the result of relatively large energy-dependent anharmonic effects which have opposite sign, leading to a total contribution near zero.

Authors:
 [1];  [1];  [1];  [2]; ORCiD logo [1];  [3]; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Missouri Univ. of Science and Technology, Rolla, MO (United States)
  3. Idaho National Lab. (INL), Idaho Falls, ID (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1530058
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review Materials
Additional Journal Information:
Journal Volume: 3; Journal Issue: 6; Journal ID: ISSN 2475-9953
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Bryan, M. S., Pang, J. W. L., Larson, B. C., Chernatynskiy, A., Abernathy, D. L., Gofryk, K., and Manley, M. E. Impact of anharmonicity on the vibrational entropy and specific heat of UO2. United States: N. p., 2019. Web. doi:10.1103/PhysRevMaterials.3.065405.
Bryan, M. S., Pang, J. W. L., Larson, B. C., Chernatynskiy, A., Abernathy, D. L., Gofryk, K., & Manley, M. E. Impact of anharmonicity on the vibrational entropy and specific heat of UO2. United States. doi:10.1103/PhysRevMaterials.3.065405.
Bryan, M. S., Pang, J. W. L., Larson, B. C., Chernatynskiy, A., Abernathy, D. L., Gofryk, K., and Manley, M. E. Fri . "Impact of anharmonicity on the vibrational entropy and specific heat of UO2". United States. doi:10.1103/PhysRevMaterials.3.065405.
@article{osti_1530058,
title = {Impact of anharmonicity on the vibrational entropy and specific heat of UO2},
author = {Bryan, M. S. and Pang, J. W. L. and Larson, B. C. and Chernatynskiy, A. and Abernathy, D. L. and Gofryk, K. and Manley, M. E.},
abstractNote = {The impact of anharmonicity on the vibrational entropy and heat capacity of UO2 has been discovered from 10 to 1200 K using inelastic neutron-scattering measurements of the phonon density of states (PDOS). Small changes in the PDOS are observed from 10 to 295 K, with more noticeable changes appearing in the 750- and 1200-K data. The specific heat determined from the PDOS measurements is in agreement with macroscopic specific heat measurements, and the overall impact of nondilation anharmonicity on the specific heat has been shown to be less than 2%. An analysis of the phonon measurements shows that the softening of acoustic phonons with temperature is consistent with the quasiharmonic approximation. The optical phonons deviate from the quasiharmonic prediction, with the low-energy optical phonons between approximately 20 and 50 meV softening more than expected, while the higher-energy optical phonons between approximately 50 and 80 meV have no appreciable softening over the temperature range measured. The observation of a small anharmonic specific heat contribution has been demonstrated to be the result of relatively large energy-dependent anharmonic effects which have opposite sign, leading to a total contribution near zero.},
doi = {10.1103/PhysRevMaterials.3.065405},
journal = {Physical Review Materials},
number = 6,
volume = 3,
place = {United States},
year = {2019},
month = {6}
}

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This content will become publicly available on June 28, 2020
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