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Title: Phonons in Si 24 at simultaneously elevated temperature and pressure

Journal Article · · Physical Review B
 [1];  [1];  [1];  [2];  [2];  [3]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  2. Carnegie Inst. of Washington, Washington, DC (United States)
  3. 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
Citation Metrics:
Cited by: 4 works
Citation information provided by
Web of Science

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