| About this Abstract |
| Meeting |
2020 TMS Annual Meeting & Exhibition
|
| Symposium
|
Computational Thermodynamics and Kinetics
|
| Presentation Title |
The Anharmonic Origin of the Large Thermal Expansion of NaBr |
| Author(s) |
Yang Shen, Claire Saunders, Camille Bernal, Douglas Abernathy, Michael Manley, Brent Fultz |
| On-Site Speaker (Planned) |
Yang Shen |
| Abstract Scope |
For most elements and simple compounds, the free energy originates from an elastic energy that changes with volume, and a vibrational entropy that depends on the occupancies and frequencies of phonon modes. In the quasiharmonic approximation (QHA), the phonon frequencies depend only on V, and on T only insofar as it alters V by thermal expansion, assuming that the T-dependence of phonon frequencies alone gives small corrections to the QHA result. Here we show how INS measurements on a single crystal of NaBr reveal an unqualified failure of the QHA to predict the thermal expansion. Ab initio computations with nuclear quantum effects successfully predicted both the phonon dispersions and the large thermal expansion of NaBr. The frequencies of longitudinal-optical phonon modes decrease significantly with temperature owing to the real part of the phonon self-energy. This originates from the cubic interactions associated with triplets along the direction of nearest-neighbor Na-Br bonds. |
| Proceedings Inclusion? |
Planned: Supplemental Proceedings volume |