Abstract:
:Despite the widespread use of silicon in modern technology, its peculiar thermal expansion is not well understood. Adapting harmonic phonons to the specific volume at temperature, the quasiharmonic approximation, has become accepted for simulating the thermal expansion, but has given ambiguous interpretations for microscopic mechanisms. To test atomistic mechanisms, we performed inelastic neutron scattering experiments from 100 K to 1,500 K on a single crystal of silicon to measure the changes in phonon frequencies. Our state-of-the-art ab initio calculations, which fully account for phonon anharmonicity and nuclear quantum effects, reproduced the measured shifts of individual phonons with temperature, whereas quasiharmonic shifts were mostly of the wrong sign. Surprisingly, the accepted quasiharmonic model was found to predict the thermal expansion owing to a large cancellation of contributions from individual phonons.
journal_name
Proc Natl Acad Sci U S Aauthors
Kim DS,Hellman O,Herriman J,Smith HL,Lin JYY,Shulumba N,Niedziela JL,Li CW,Abernathy DL,Fultz Bdoi
10.1073/pnas.1707745115subject
Has Abstractpub_date
2018-02-27 00:00:00pages
1992-1997issue
9eissn
0027-8424issn
1091-6490pii
1707745115journal_volume
115pub_type
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