| About this Abstract |
| Meeting |
2021 TMS Annual Meeting & Exhibition
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| Symposium
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Hume-Rothery Symposium: Accelerated Measurements and Predictions of Thermodynamics and Kinetics for Materials Design and Discovery
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| Presentation Title |
Phonon Anharmonicity Causes the Large Thermal Expansion of NaBr |
| Author(s) |
Brent T. Fultz, Yang Shen, Claire Saunders, Camille Bernal, Michael Manley |
| On-Site Speaker (Planned) |
Brent T. Fultz |
| Abstract Scope |
Thermal expansion can be understood as a balance between phonon entropy S and elastic energy E in setting the minimum of the free energy F(V,T). For rocksalt NaBr, all the entropy is from phonons. Phonon frequencies depend on both V and T, but the conventional quasiharmonic approximation (QHA) uses V alone. We measured all phonons in a crystal of rocksalt NaBr with the ARCS inelastic neutron spectrometer. These INS measurements show an unqualified failure of the QHA to predict the temperature dependence of phonon frequencies in NaBr, even below room temperature. The QHA also fails to predict the correct thermal expansion. Anharmonic theory, using ab initio DFT calculations (VASP with s-TDEP), was much more successful. The longitudinal-optical phonon modes of NaBr have broadenings in frequency that are nearly as large as their thermal shifts. The large cubic anharmonicity originates with nearest-neighbor Na-Br bonds. [Y. Shen, et al., arXiv:1909.03150v1 (2019] |
| Proceedings Inclusion? |
Planned: |