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

Journal Article · · Physical Review Materials

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.

Research Organization:
Energy Frontier Research Centers (EFRC) (United States). Center for Thermal Energy Transport under Irradiation (TETI); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1530058
Alternate ID(s):
OSTI ID: 1546418; OSTI ID: 1558431
Journal Information:
Physical Review Materials, Journal Name: Physical Review Materials Journal Issue: 6 Vol. 3; ISSN PRMHAR; ISSN 2475-9953
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

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