Wei, B.; Cai, Q.; Sun, Q.; Su, Y.; Said, A. H.; Abernathy, D. L.; Li, J. Hong C.
Matryoshka Phonon Twining in a-GaN Journal Article
In: Communications Physics, vol. 4, no. 227, 2021.
Abstract | Links | BibTeX | Tags: lattice expansion, metal-insulator transition, phonon, thermal transport
@article{Li2021,
title = {Matryoshka Phonon Twining in a-GaN},
author = {B. Wei and Q. Cai and Q. Sun and Y. Su and A. H. Said and D. L. Abernathy and J. Hong
C. Li},
url = {https://www.nature.com/articles/s42005-021-00727-9},
doi = {10.1038/s42005-021-00727-9},
year = {2021},
date = {2021-10-12},
urldate = {2021-07-01},
journal = {Communications Physics},
volume = {4},
number = {227},
abstract = {Understanding lattice dynamics is crucial for effective thermal management in electronic devices because phonons dominate thermal transport in most semiconductors. α-GaN has become a focus of interest as one of the most important third-generation power semiconductors, however, the knowledge on its phonon dynamics remains limited. Here we show a Matryoshka phonon dispersion of α-GaN with the complementary inelastic X-ray and neutron scattering techniques and the first-principles calculations. Such Matryoshka twinning throughout the basal plane of the reciprocal space is demonstrated to amplify the anharmonicity of the related phonons through creating abundant three-phonon scattering channels and cutting the lifetime of affected modes by more than 50%. Such phonon topology contributes to reducing the in-plane thermal transport, thus the anisotropic thermal conductivity of α-GaN. The results not only have implications for engineering the thermal performance of α-GaN, but also offer valuable insights on the role of anomalous phonon topology in thermal transport of other technically semiconductors.},
keywords = {lattice expansion, metal-insulator transition, phonon, thermal transport},
pubstate = {published},
tppubtype = {article}
}
Understanding lattice dynamics is crucial for effective thermal management in electronic devices because phonons dominate thermal transport in most semiconductors. α-GaN has become a focus of interest as one of the most important third-generation power semiconductors, however, the knowledge on its phonon dynamics remains limited. Here we show a Matryoshka phonon dispersion of α-GaN with the complementary inelastic X-ray and neutron scattering techniques and the first-principles calculations. Such Matryoshka twinning throughout the basal plane of the reciprocal space is demonstrated to amplify the anharmonicity of the related phonons through creating abundant three-phonon scattering channels and cutting the lifetime of affected modes by more than 50%. Such phonon topology contributes to reducing the in-plane thermal transport, thus the anisotropic thermal conductivity of α-GaN. The results not only have implications for engineering the thermal performance of α-GaN, but also offer valuable insights on the role of anomalous phonon topology in thermal transport of other technically semiconductors.
Smith, Hillary L.; Shen, Yang; Kim, Dennis S.; Yang, Fred C.; Adams, C. P.; Li, Chen W.; Abernathy, D. L.; Stone, M. B.; Fultz, B.
Temperature dependence of phonons in FeGe2 Journal Article
In: Physical Review Materials, vol. 2, pp. 103602, 2018.
Abstract | Links | BibTeX | Tags: anharmonicity, high temperature, lattice expansion, magnetism, phonon, vibrational entropy
@article{Smith2018,
title = {Temperature dependence of phonons in FeGe2},
author = {Hillary L. Smith and Yang Shen and Dennis S. Kim and Fred C. Yang and C.P. Adams and Chen W. Li and D.L. Abernathy and M.B. Stone and B. Fultz},
url = {https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.2.103602},
doi = {10.1103/PhysRevMaterials.2.103602},
year = {2018},
date = {2018-10-09},
journal = {Physical Review Materials},
volume = {2},
pages = {103602},
abstract = {Inelastic neutron scattering was used to measure phonon dispersions in a single crystal of FeGe2 with the C16 structure at 300, 500, and 635 K. Phonon densities of states (DOS) were also measured on polycrystalline FeGe2 from 325 to 1050 K, and the Fe partial DOS was obtained from polycrystalline
57 FeGe2 at 300 K using nuclear resonant inelastic x-ray scattering. The dominant feature in the temperature dependence of the phonon spectrum is thermal broadening of high-energy modes. The energy shifts of the low- and high-energy parts of the spectrum were almost the same. DFT calculations performed with the quasiharmonic approximation gave results in moderate agreement with the experimental thermal energy shifts, although the isobaric Gr\"{u}neisen parameter calculated from the quasiharmonic model was smaller than that from measurements. The thermal broadening of the phonon spectrum and dispersions, especially at high energies, indicates a cubic anharmonicity to second order that should also induce phonon shifts. We show that different anharmonic contributions cancel out, giving average phonon shifts in moderate agreement to calculations with the quasiharmonic approximation. The different parts of the large phonon contribution to the entropy are separated for FeGe2, showing modest but interpretable anharmonic contributions.},
keywords = {anharmonicity, high temperature, lattice expansion, magnetism, phonon, vibrational entropy},
pubstate = {published},
tppubtype = {article}
}
Inelastic neutron scattering was used to measure phonon dispersions in a single crystal of FeGe2 with the C16 structure at 300, 500, and 635 K. Phonon densities of states (DOS) were also measured on polycrystalline FeGe2 from 325 to 1050 K, and the Fe partial DOS was obtained from polycrystalline
57 FeGe2 at 300 K using nuclear resonant inelastic x-ray scattering. The dominant feature in the temperature dependence of the phonon spectrum is thermal broadening of high-energy modes. The energy shifts of the low- and high-energy parts of the spectrum were almost the same. DFT calculations performed with the quasiharmonic approximation gave results in moderate agreement with the experimental thermal energy shifts, although the isobaric Grüneisen parameter calculated from the quasiharmonic model was smaller than that from measurements. The thermal broadening of the phonon spectrum and dispersions, especially at high energies, indicates a cubic anharmonicity to second order that should also induce phonon shifts. We show that different anharmonic contributions cancel out, giving average phonon shifts in moderate agreement to calculations with the quasiharmonic approximation. The different parts of the large phonon contribution to the entropy are separated for FeGe2, showing modest but interpretable anharmonic contributions.
57 FeGe2 at 300 K using nuclear resonant inelastic x-ray scattering. The dominant feature in the temperature dependence of the phonon spectrum is thermal broadening of high-energy modes. The energy shifts of the low- and high-energy parts of the spectrum were almost the same. DFT calculations performed with the quasiharmonic approximation gave results in moderate agreement with the experimental thermal energy shifts, although the isobaric Grüneisen parameter calculated from the quasiharmonic model was smaller than that from measurements. The thermal broadening of the phonon spectrum and dispersions, especially at high energies, indicates a cubic anharmonicity to second order that should also induce phonon shifts. We show that different anharmonic contributions cancel out, giving average phonon shifts in moderate agreement to calculations with the quasiharmonic approximation. The different parts of the large phonon contribution to the entropy are separated for FeGe2, showing modest but interpretable anharmonic contributions.
Kim, D. S.; Hellman, O.; Herriman, J.; Smith, H. L.; Lin, J. Y. Y.; Shulumba, N.; Niedziela, J. L.; Li, C. W.; Abernathy, D. L.; Fultz, B.
Nuclear quantum effect with pure anharmonicity and the anomalous thermal expansion of silicon Journal Article
In: Proceedings of the National Academy of Sciences, vol. 115, no. 9, pp. 1992, 2018.
Abstract | Links | BibTeX | Tags: anharmonicity, first-principles, high temperature, lattice expansion
@article{Kim2018,
title = {Nuclear quantum effect with pure anharmonicity and the anomalous thermal expansion of silicon},
author = {D. S. Kim and O. Hellman and J. Herriman and H. L. Smith and J. Y. Y. Lin and N. Shulumba and J. L. Niedziela and C. W. Li and D. L. Abernathy and B. Fultz},
url = {https://www.pnas.org/content/115/9/1992},
doi = {10.1073/pnas.1707745115},
year = {2018},
date = {2018-02-27},
journal = {Proceedings of the National Academy of Sciences},
volume = {115},
number = {9},
pages = {1992},
abstract = {Despite the widespread use of silicon in modern technology, its peculiar thermal expansion is not well understood. Adapt- ing harmonic phonons to the specific volume at temperature, the quasiharmonic approximation, has become accepted for sim- ulating the thermal expansion, but has given ambiguous inter- pretations for microscopic mechanisms. To test atomistic mech- anisms, we performed inelastic neutron scattering experiments from 100 K to 1,500 K on a single crystal of silicon to mea- sure the changes in phonon frequencies. Our state-of-the-art ab initio calculations, which fully account for phonon anharmonic- ity 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 expan- sion owing to a large cancellation of contributions from individual phonons.},
keywords = {anharmonicity, first-principles, high temperature, lattice expansion},
pubstate = {published},
tppubtype = {article}
}
Despite the widespread use of silicon in modern technology, its peculiar thermal expansion is not well understood. Adapt- ing harmonic phonons to the specific volume at temperature, the quasiharmonic approximation, has become accepted for sim- ulating the thermal expansion, but has given ambiguous inter- pretations for microscopic mechanisms. To test atomistic mech- anisms, we performed inelastic neutron scattering experiments from 100 K to 1,500 K on a single crystal of silicon to mea- sure the changes in phonon frequencies. Our state-of-the-art ab initio calculations, which fully account for phonon anharmonic- ity 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 expan- sion owing to a large cancellation of contributions from individual phonons.
Lan, T; Li, Chen W; Hellman, O; Kim, D S; Munoz, J A; Smith, H L; Abernathy, D L; Fultz, B
Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion and its stabilization of rutile TiO2 Journal Article
In: Physical Review B, vol. 92, no. 5, 2015.
Links | BibTeX | Tags: anharmonicity, lattice, lattice expansion, oxide, phonon
@article{Lan:2015bs,
title = {Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion and its stabilization of rutile TiO2},
author = {T Lan and Chen W Li and O Hellman and D S Kim and J A Munoz and H L Smith and D L Abernathy and B Fultz},
url = {http://link.aps.org/doi/10.1103/PhysRevB.92.054304},
doi = {10.1103/PhysRevB.92.054304},
year = {2015},
date = {2015-01-01},
journal = {Physical Review B},
volume = {92},
number = {5},
keywords = {anharmonicity, lattice, lattice expansion, oxide, phonon},
pubstate = {published},
tppubtype = {article}
}
Kim, D S; Smith, H L; Niedziela, J L; Li, Chen W; Abernathy, D L; Fultz, B
Phonon anharmonicity in silicon from 100 to 1500 K Journal Article
In: Physical Review B, vol. 91, no. 1, pp. 014307, 2015.
Links | BibTeX | Tags: anharmonicity, lattice, lattice expansion, phonon
@article{Kim:2015fx,
title = {Phonon anharmonicity in silicon from 100 to 1500 K},
author = {D S Kim and H L Smith and J L Niedziela and Chen W Li and D L Abernathy and B Fultz},
url = {https://link.aps.org/doi/10.1103/PhysRevB.91.014307},
doi = {10.1103/PhysRevB.91.014307},
year = {2015},
date = {2015-01-01},
journal = {Physical Review B},
volume = {91},
number = {1},
pages = {014307},
keywords = {anharmonicity, lattice, lattice expansion, phonon},
pubstate = {published},
tppubtype = {article}
}
Li, Chen W; Tang, X; Munoz, J A; Keith, J B; Tracy, S J; Abernathy, D L; Fultz, B
Structural Relationship between Negative Thermal Expansion and Quartic Anharmonicity of Cubic ScF3 Journal Article
In: Physical Review Letters, vol. 107, no. 19, pp. 195504, 2011.
Links | BibTeX | Tags: anharmonicity. fluoride, lattice expansion, NTE, phonon
@article{li_structural_2011,
title = {Structural Relationship between Negative Thermal Expansion and Quartic Anharmonicity of Cubic ScF3},
author = {Chen W Li and X Tang and J A Munoz and J B Keith and S J Tracy and D L Abernathy and B Fultz},
url = {https://link.aps.org/doi/10.1103/PhysRevLett.107.195504},
doi = {10.1103/PhysRevLett.107.195504},
year = {2011},
date = {2011-01-01},
journal = {Physical Review Letters},
volume = {107},
number = {19},
pages = {195504},
keywords = {anharmonicity. fluoride, lattice expansion, NTE, phonon},
pubstate = {published},
tppubtype = {article}
}