Phonons in at simultaneously elevated temperature and pressure
- California Inst. of Technology (CalTech), Pasadena, CA (United States)
- Carnegie Inst. of Washington, Washington, DC (United States)
- Carnegie Inst. of Washington, Washington, DC (United States); Center for High Pressure Sciecne and Technology Advanced Research (HPSTAR), Shanghai (China)
Raman spectroscopy was used to measure the frequencies of phonons in Si 24 with an open clathrate structure at temperatures ranging from 80 to 400 K with simultaneous pressures of 0 to 8 GPa. The frequency shifts of the different phonons were substantially different under either temperature or pressure. The quasiharmonic behavior was isolated by varying pressure at low temperatures, and the anharmonic behavior was isolated by varying temperature at low pressures. Phonon modes dominated by bond bending were anomalous, showing stiffening with temperature and softening with pressure. Both the quasiharmonic behavior and the anharmonic behavior changed markedly with simultaneous changes in temperature Δ T and pressure Δ P . With Δ T = 320 K and Δ P = 8 GPa , some frequency shifts that scaled with the product Δ T Δ P were as large as the shifts from Δ T and Δ P alone. The thermodynamic entropy of this material likely has a dependence on Δ T and Δ P that cannot be obtained by adding effects from quasiharmonicity and phonon-phonon anharmonicity.
- Research Organization:
- Energy Frontier Research Centers (EFRC) (United States). Energy Frontier Research in Extreme Environments (EFree)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- SC0001057
- OSTI ID:
- 1388065
- Alternate ID(s):
- OSTI ID: 1347809
- Journal Information:
- Physical Review B, Vol. 95, Issue 9; Related Information: EFree partners with Carnegie Institution of Washington (lead); California Institute of Technology; Colorado School of Mines; Cornell University; Lehigh University; Pennsylvania State University; ISSN 2469-9950
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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