He, L; Li, Chen W; Hamilton, W A; Hong, T; Tong, X; Winn, B L; Crow, L; Bailey, K; Gallego, N C Anomalous neutron scattering ‘halo’ observed in highly oriented pyrolytic graphite Journal Article Journal of Applied Cyrstallography, 52 (2), pp. 296-303, 2019. Abstract | Links | BibTeX | Tags: graphite, neutron scattering, phonon @article{He2019, title = {Anomalous neutron scattering ‘halo’ observed in highly oriented pyrolytic graphite}, author = {L. He and Chen W. Li and W.A. Hamilton and T. Hong and X. Tong and B.L. Winn and L. Crow and K. Bailey and N.C. Gallego}, url = {https://onlinelibrary.wiley.com/iucr/doi/10.1107/S1600576719001110}, doi = {10.1107/S1600576719001110}, year = {2019}, date = {2019-03-05}, journal = {Journal of Applied Cyrstallography}, volume = {52}, number = {2}, pages = {296-303}, abstract = {Highly oriented pyrolytic graphite (HOPG) has been used as monochromators, analyzers and filters at neutron and X-ray scattering facilities for more than half a century. Interesting questions remain. In this work, the first observation of anomalous neutron ‘halo’ scattering of HOPG is reported. The scattering projects a ring onto the detector with a half-cone angle of 12.4, which surprisingly persists to incident neutron wavelengths far beyond the Bragg cutoff for graphite (6.71 A ̊ ). At longer wavelengths the ring is clearly a doublet with a splitting roughly proportional to wavelength. Sample tilting leads to the shift of the ring, which is wavelength dependent with longer wavelengths providing a smaller difference between the ring shift and the sample tilting. The ring broadens and weakens with decreasing HOPG quality. The lattice dynamics of graphite play a role in causing the scattering ring, as shown by the fact that the ring vanishes once the sample is cooled to 30 K. A possible interpretation by multiple scattering including elastic and inelastic processes is proposed.}, keywords = {graphite, neutron scattering, phonon}, pubstate = {published}, tppubtype = {article} } Highly oriented pyrolytic graphite (HOPG) has been used as monochromators, analyzers and filters at neutron and X-ray scattering facilities for more than half a century. Interesting questions remain. In this work, the first observation of anomalous neutron ‘halo’ scattering of HOPG is reported. The scattering projects a ring onto the detector with a half-cone angle of 12.4, which surprisingly persists to incident neutron wavelengths far beyond the Bragg cutoff for graphite (6.71 A ̊ ). At longer wavelengths the ring is clearly a doublet with a splitting roughly proportional to wavelength. Sample tilting leads to the shift of the ring, which is wavelength dependent with longer wavelengths providing a smaller difference between the ring shift and the sample tilting. The ring broadens and weakens with decreasing HOPG quality. The lattice dynamics of graphite play a role in causing the scattering ring, as shown by the fact that the ring vanishes once the sample is cooled to 30 K. A possible interpretation by multiple scattering including elastic and inelastic processes is proposed. |
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 Physical Review Materials, 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 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.}, 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. |
Smith, H L; Li, Chen W; Hoff, A; Garrett, G R; Kim, D S; Yang, F C; Lucas, M S; Swan-Wood, T; Lin, J Y Y; Stone, M B; Abernathy, D L; Demetriou, M D; Fultz, B Separating the configurational and vibrational entropy contributions in metallic glasses Journal Article Nature Physics, 13 (9), pp. 900-905, 2017. Links | BibTeX | Tags: metallic glass, neutron, phase transition, phonon, thermodynamics, vibrational entropy @article{Smith:2017goa, title = {Separating the configurational and vibrational entropy contributions in metallic glasses}, author = {H L Smith and Chen W Li and A Hoff and G R Garrett and D S Kim and F C Yang and M S Lucas and T Swan-Wood and J Y Y Lin and M B Stone and D L Abernathy and M D Demetriou and B Fultz}, url = {http://www.nature.com/doifinder/10.1038/nphys4142}, doi = {10.1038/nphys4142}, year = {2017}, date = {2017-01-01}, journal = {Nature Physics}, volume = {13}, number = {9}, pages = {900-905}, keywords = {metallic glass, neutron, phase transition, phonon, thermodynamics, vibrational entropy}, pubstate = {published}, tppubtype = {article} } |
Shen, Yang ; Li, Chen W; Tang, Xiaoli ; Smith, Hillary L; Fultz, B honon anharmonicity and components of the entropy in palladium and platinum Journal Article Physical Review B, 93 , pp. 214303, 2016. Abstract | Links | BibTeX | Tags: anharmonicity, neutron, phonon, vibrational entropy @article{Shen2016, title = {honon anharmonicity and components of the entropy in palladium and platinum}, author = {Shen, Yang and Li, Chen W. and Tang, Xiaoli and Smith, Hillary L. and Fultz, B.}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.93.214303}, doi = {10.1103/PhysRevB.93.214303}, year = {2016}, date = {2016-06-07}, journal = {Physical Review B}, volume = {93}, pages = {214303}, abstract = {Inelastic neutron scattering was used to measure the phonon density of states in fcc palladium and platinum metal at temperatures from 7 K to 1576 K. Both phonon-phonon interactions and electron-phonon interactions were calculated by methods based on density functional theory (DFT) and were consistent with the measured shifts and broadenings of phonons with temperature. Unlike the longitudinal modes, the characteristic transverse modes had a nonlinear dependence on temperature owing to the requirement for a population of thermal phonons for upscattering. Kohn anomalies were observed in the measurements at low temperature and were reproduced by calculations based on DFT. Contributions to the entropy from phonons and electrons were assessed and summed to obtain excellent agreement with prior calorimetric data. The entropy from thermal expansion is positive for both phonons and electrons but larger for phonons. The anharmonic phonon entropy is negative in Pt, but in Pd it changes from positive to negative with increasing temperature. Owing to the position of the Fermi level on the electronic DOS, the electronic entropy was sensitive to the adiabatic electron-phonon interaction in both Pd and Pt. The adiabatic EPI depended strongly on thermal atom displacements.}, keywords = {anharmonicity, neutron, phonon, vibrational entropy}, pubstate = {published}, tppubtype = {article} } Inelastic neutron scattering was used to measure the phonon density of states in fcc palladium and platinum metal at temperatures from 7 K to 1576 K. Both phonon-phonon interactions and electron-phonon interactions were calculated by methods based on density functional theory (DFT) and were consistent with the measured shifts and broadenings of phonons with temperature. Unlike the longitudinal modes, the characteristic transverse modes had a nonlinear dependence on temperature owing to the requirement for a population of thermal phonons for upscattering. Kohn anomalies were observed in the measurements at low temperature and were reproduced by calculations based on DFT. Contributions to the entropy from phonons and electrons were assessed and summed to obtain excellent agreement with prior calorimetric data. The entropy from thermal expansion is positive for both phonons and electrons but larger for phonons. The anharmonic phonon entropy is negative in Pt, but in Pd it changes from positive to negative with increasing temperature. Owing to the position of the Fermi level on the electronic DOS, the electronic entropy was sensitive to the adiabatic electron-phonon interaction in both Pd and Pt. The adiabatic EPI depended strongly on thermal atom displacements. |
Bansal, D; Hong, J; Li, Chen W; May, A F; Porter, W; Hu, M Y; Abernathy, D L; Delaire, O Phonon anharmonicity and negative thermal expansion in SnSe Journal Article Physical Review B, 94 (5), pp. 054307, 2016. Links | BibTeX | Tags: neutron, NTE, phonon, selenide, thermodynamics, thermoelectric @article{Bansal:2016hd, title = {Phonon anharmonicity and negative thermal expansion in SnSe}, author = {D Bansal and J Hong and Chen W Li and A F May and W Porter and M Y Hu and D L Abernathy and O Delaire}, url = {https://link.aps.org/doi/10.1103/PhysRevB.94.054307}, doi = {10.1103/PhysRevB.94.054307}, year = {2016}, date = {2016-01-01}, journal = {Physical Review B}, volume = {94}, number = {5}, pages = {054307}, keywords = {neutron, NTE, phonon, selenide, thermodynamics, thermoelectric}, pubstate = {published}, tppubtype = {article} } |
Li, Chen W; Smith, H L; Lan, T; Niedziela, J L; Munoz, J A; Keith, J B; Mauger, L; Abernathy, D L; Fultz, B Phonon anharmonicity of monoclinic zirconia and yttrium-stabilized zirconia Journal Article Physical Review B, 91 (14), pp. 5563, 2015. Links | BibTeX | Tags: anharmonicity, oxide, phonon @article{li_phonon_2015, title = {Phonon anharmonicity of monoclinic zirconia and yttrium-stabilized zirconia}, author = {Chen W Li and H L Smith and T Lan and J L Niedziela and J A Munoz and J B Keith and L Mauger and D L Abernathy and B Fultz}, url = {https://link.aps.org/doi/10.1103/PhysRevB.91.144302}, doi = {10.1103/PhysRevB.91.144302}, year = {2015}, date = {2015-04-01}, journal = {Physical Review B}, volume = {91}, number = {14}, pages = {5563}, keywords = {anharmonicity, oxide, phonon}, pubstate = {published}, tppubtype = {article} } |
Delaire, O; Al-Qasir, I I; May, A F; Li, Chen W; Sales, B C; Niedziela, J L; Ma, J; Matsuda, M; Abernathy, D L; Berlijn, T Heavy-impurity resonance, hybridization, and phonon spectral functions in Fe1−xMxSi (M=Ir, Os) Journal Article Physical Review B, 91 (9), pp. 784, 2015. Links | BibTeX | Tags: anharmonicity, lattice dynamics, phonon @article{delaire_heavy-impurity_2015, title = {Heavy-impurity resonance, hybridization, and phonon spectral functions in Fe1−xMxSi (M=Ir, Os)}, author = {O Delaire and I I Al-Qasir and A F May and Chen W Li and B C Sales and J L Niedziela and J Ma and M Matsuda and D L Abernathy and T Berlijn}, url = {https://link.aps.org/doi/10.1103/PhysRevB.91.094307}, doi = {10.1103/PhysRevB.91.094307}, year = {2015}, date = {2015-03-01}, journal = {Physical Review B}, volume = {91}, number = {9}, pages = {784}, keywords = {anharmonicity, lattice dynamics, phonon}, pubstate = {published}, tppubtype = {article} } |
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 Physical Review B, 92 (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} } |
Bansal, D; Li, Chen W; Said, A H; Abernathy, D L; Yan, J Electron-phonon coupling and thermal transport in the thermoelectric compound Mo3Sb7−xTex Journal Article Physical Review B, 92 (21), pp. 214301, 2015. Links | BibTeX | Tags: electron-phonon coupling, phonon, thermal transport, thermoelectric @article{bansal_electron-phonon_2015-2, title = {Electron-phonon coupling and thermal transport in the thermoelectric compound Mo3Sb7−xTex}, author = {D Bansal and Chen W Li and A H Said and D L Abernathy and J Yan}, url = {https://link.aps.org/doi/10.1103/PhysRevB.92.214301}, doi = {10.1103/PhysRevB.92.214301}, year = {2015}, date = {2015-01-01}, journal = {Physical Review B}, volume = {92}, number = {21}, pages = {214301}, keywords = {electron-phonon coupling, phonon, thermal transport, thermoelectric}, 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 Physical Review B, 91 (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} } |
Budai, J D; Hong, J; Manley, M E; Specht, E D; Li, Chen W; Tischler, J Z; Abernathy, D L; Said, A H; Leu, B M; Boatner, L A; McQueeney, R J; Delaire, O Metallization of vanadium dioxide driven by large phonon entropy Journal Article Nature, 515 (7528), pp. 535-539, 2014. Links | BibTeX | Tags: anharmonicity, metal-insulator transition, neutron, phonon, synchrotron, thermodynamics, vibrational entropy @article{budai_metallization_2014, title = {Metallization of vanadium dioxide driven by large phonon entropy}, author = {J D Budai and J Hong and M E Manley and E D Specht and Chen W Li and J Z Tischler and D L Abernathy and A H Said and B M Leu and L A Boatner and R J McQueeney and O Delaire}, url = {http://www.nature.com/doifinder/10.1038/nature13865}, doi = {10.1038/nature13865}, year = {2014}, date = {2014-11-01}, journal = {Nature}, volume = {515}, number = {7528}, pages = {535-539}, keywords = {anharmonicity, metal-insulator transition, neutron, phonon, synchrotron, thermodynamics, vibrational entropy}, pubstate = {published}, tppubtype = {article} } |
Lan, T; Li, Chen W; Niedziela, J L; Smith, H L; Abernathy, D L; Rossman, G R; Fultz, B Anharmonic lattice dynamics of Ag2O studied by inelastic neutron scattering and first-principles molecular dynamics simulations Journal Article Physical Review B, 89 (5), pp. 2022, 2014. Links | BibTeX | Tags: anharmonicity, neutron, oxide, phonon @article{lan_anharmonic_2014, title = {Anharmonic lattice dynamics of Ag2O studied by inelastic neutron scattering and first-principles molecular dynamics simulations}, author = {T Lan and Chen W Li and J L Niedziela and H L Smith and D L Abernathy and G R Rossman and B Fultz}, url = {https://link.aps.org/doi/10.1103/PhysRevB.89.054306}, doi = {10.1103/PhysRevB.89.054306}, year = {2014}, date = {2014-01-01}, journal = {Physical Review B}, volume = {89}, number = {5}, pages = {2022}, keywords = {anharmonicity, neutron, oxide, phonon}, pubstate = {published}, tppubtype = {article} } |
Li, Chen W; Ma, J; Cao, H B; May, A F; Abernathy, D L; Ehlers, G; Hoffmann, C; Wang, X; Hong, T; Huq, A; Gourdon, O; Delaire, O Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics Journal Article Physical Review B, 90 (21), pp. 194, 2014. Links | BibTeX | Tags: anharmonicity, lattice dynamics, neutron, phonon, telluride @article{li_anharmonicity_2014, title = {Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics}, author = {Chen W Li and J Ma and H B Cao and A F May and D L Abernathy and G Ehlers and C Hoffmann and X Wang and T Hong and A Huq and O Gourdon and O Delaire}, url = {https://link.aps.org/doi/10.1103/PhysRevB.90.214303}, doi = {10.1103/PhysRevB.90.214303}, year = {2014}, date = {2014-01-01}, journal = {Physical Review B}, volume = {90}, number = {21}, pages = {194}, keywords = {anharmonicity, lattice dynamics, neutron, phonon, telluride}, pubstate = {published}, tppubtype = {article} } |
Li, Chen W; Hellman, O; Ma, J; May, A F; Cao, H B; Chen, X; Christianson, A D; Ehlers, G; Singh, D J; Sales, B C; Delaire, O Phonon Self-Energy and Origin of Anomalous Neutron Scattering Spectra in SnTe and PbTe Thermoelectrics Journal Article Physical Review Letters, 112 (17), pp. 194, 2014. Links | BibTeX | Tags: anharmonicity, neutron, phonon, thermoelectric @article{li_phonon_2014, title = {Phonon Self-Energy and Origin of Anomalous Neutron Scattering Spectra in SnTe and PbTe Thermoelectrics}, author = {Chen W Li and O Hellman and J Ma and A F May and H B Cao and X Chen and A D Christianson and G Ehlers and D J Singh and B C Sales and O Delaire}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.112.175501}, doi = {10.1103/PhysRevLett.112.175501}, year = {2014}, date = {2014-01-01}, journal = {Physical Review Letters}, volume = {112}, number = {17}, pages = {194}, keywords = {anharmonicity, neutron, phonon, thermoelectric}, pubstate = {published}, tppubtype = {article} } |
Lan, T; Li, Chen W; Fultz, B Physical Review B, 86 (13), pp. 134302, 2012. Abstract | Links | BibTeX | Tags: anharmonicity, first-principles, phonon, Raman @article{lan_phonon_2012, title = {Phonon anharmonicity of rutile SnO 2studied by Raman spectrometry and first principles calculations of the kinematics of phonon-phonon interactions}, author = {T Lan and Chen W Li and B Fultz}, url = {https://link.aps.org/doi/10.1103/PhysRevB.86.134302}, doi = {10.1103/PhysRevB.86.134302}, year = {2012}, date = {2012-10-01}, journal = {Physical Review B}, volume = {86}, number = {13}, pages = {134302}, abstract = {Raman spectra of rutile tin dioxide (SnO$_2$) were measured at temperatures from 83 to 873 K. The pure anharmonicity from phonon-phonon interactions was found to be large and comparable to the quasiharmonicity. First-principles calculations of phonon dispersions were used to assess the kinematics of three-phonon and four-phonon processes. These kinematics were used to generate Raman peak widths and shifts, which were fit to measured data to obtain the cubic and quartic components of the anharmonicity for each Raman mode. The $B_2g$ mode had a large quartic component, consistent with the symmetry of its atom displacements. The broadening of the $B_2g$ mode with temperature showed an unusual concave-downwards curvature. This curvature is caused by a change with temperature in the number of down-conversion decay channels, originating with the wide band gap in the phonon dispersions.}, keywords = {anharmonicity, first-principles, phonon, Raman}, pubstate = {published}, tppubtype = {article} } Raman spectra of rutile tin dioxide (SnO$_2$) were measured at temperatures from 83 to 873 K. The pure anharmonicity from phonon-phonon interactions was found to be large and comparable to the quasiharmonicity. First-principles calculations of phonon dispersions were used to assess the kinematics of three-phonon and four-phonon processes. These kinematics were used to generate Raman peak widths and shifts, which were fit to measured data to obtain the cubic and quartic components of the anharmonicity for each Raman mode. The $B_2g$ mode had a large quartic component, consistent with the symmetry of its atom displacements. The broadening of the $B_2g$ mode with temperature showed an unusual concave-downwards curvature. This curvature is caused by a change with temperature in the number of down-conversion decay channels, originating with the wide band gap in the phonon dispersions. |
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 Physical Review Letters, 107 (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} } |
Markovskiy, N D; Munoz, J A; Lucas, M S; Li, Chen W; Delaire, O; Stone, M B; Abernathy, D L; Fultz, B Nonharmonic phonons in MgB 2at elevated temperatures Journal Article Physical Review B, 83 (17), pp. 174301, 2011. Abstract | Links | BibTeX | Tags: anharmonicity, high temperature, MgB2, phonon @article{markovskiy_nonharmonic_2011, title = {Nonharmonic phonons in MgB 2at elevated temperatures}, author = {N D Markovskiy and J A Munoz and M S Lucas and Chen W Li and O Delaire and M B Stone and D L Abernathy and B Fultz}, url = {https://link.aps.org/doi/10.1103/PhysRevB.83.174301}, doi = {10.1103/PhysRevB.83.174301}, year = {2011}, date = {2011-01-01}, journal = {Physical Review B}, volume = {83}, number = {17}, pages = {174301}, abstract = {Inelastic neutron scattering was used to measure phonon spectra in MgB$_2$ and Mg$_0.75$Al$_0.25$B$_2$ from 7 to 750 K to investigate anharmonicity and adiabatic electron-phonon coupling. First-principles calculations of phonons with a linear response method were performed at multiple unit cell volumes, and the Helmholtz free energy was minimized to obtain the lattice parameters and phonon dynamics at elevated temperature in the quasiharmonic approximation. Most of the temperature dependence of the phonon density of states could be understood with the quasiharmonic approximation, although there was also significant thermal broadening of the phonon spectra. In comparison to Mg$_0.75$Al$_0.25$B$_2$, in the energy range of 60 to 80 meV the experimental phonon spectra from MgB$_2$ showed a nonmonotonic change with temperature around 500 K. This may originate from a change with temperature of the adiabatic electron-phonon coupling.}, keywords = {anharmonicity, high temperature, MgB2, phonon}, pubstate = {published}, tppubtype = {article} } Inelastic neutron scattering was used to measure phonon spectra in MgB$_2$ and Mg$_0.75$Al$_0.25$B$_2$ from 7 to 750 K to investigate anharmonicity and adiabatic electron-phonon coupling. First-principles calculations of phonons with a linear response method were performed at multiple unit cell volumes, and the Helmholtz free energy was minimized to obtain the lattice parameters and phonon dynamics at elevated temperature in the quasiharmonic approximation. Most of the temperature dependence of the phonon density of states could be understood with the quasiharmonic approximation, although there was also significant thermal broadening of the phonon spectra. In comparison to Mg$_0.75$Al$_0.25$B$_2$, in the energy range of 60 to 80 meV the experimental phonon spectra from MgB$_2$ showed a nonmonotonic change with temperature around 500 K. This may originate from a change with temperature of the adiabatic electron-phonon coupling. |
Tang, X; Li, Chen W; Fultz, B Anharmonicity-induced phonon broadening in aluminum at high temperatures Journal Article Physical Review B, 82 (18), pp. 184301, 2010. Abstract | Links | BibTeX | Tags: Al, anharmonicity, high temperature, lifetime, phonon @article{tang_anharmonicity-induced_2010, title = {Anharmonicity-induced phonon broadening in aluminum at high temperatures}, author = {X Tang and Chen W Li and B Fultz}, url = {https://link.aps.org/doi/10.1103/PhysRevB.82.184301}, doi = {10.1103/PhysRevB.82.184301}, year = {2010}, date = {2010-11-01}, journal = {Physical Review B}, volume = {82}, number = {18}, pages = {184301}, abstract = {Thermal phonon broadening in aluminum was studied by theoretical and experimental methods. Using second-order perturbation theory, phonon linewidths from the third-order anharmonicity were calculated from first-principles density-functional theory (DFT) with the supercell finite-displacement method. The importance of all three-phonon processes were assessed and individual phonon broadenings are presented. The good agreement between calculations and prior measurements of phonon linewidths at 300 K and new measurements of the phonon density of states to 750 K indicates that the third-order phonon-phonon interactions calculated from DFT can account for the lifetime broadenings of phonons in aluminum to at least 80% of its melting temperature.}, keywords = {Al, anharmonicity, high temperature, lifetime, phonon}, pubstate = {published}, tppubtype = {article} } Thermal phonon broadening in aluminum was studied by theoretical and experimental methods. Using second-order perturbation theory, phonon linewidths from the third-order anharmonicity were calculated from first-principles density-functional theory (DFT) with the supercell finite-displacement method. The importance of all three-phonon processes were assessed and individual phonon broadenings are presented. The good agreement between calculations and prior measurements of phonon linewidths at 300 K and new measurements of the phonon density of states to 750 K indicates that the third-order phonon-phonon interactions calculated from DFT can account for the lifetime broadenings of phonons in aluminum to at least 80% of its melting temperature. |
Lucas, M S; Munoz, J A; Mauger, L; Li, Chen W; Sheets, A O; Turgut, Z; Horwath, J; Abernathy, D L; Stone, M B; Delaire, O; Xiao, Y; Fultz, B Effects of chemical composition and B2 order on phonons in bcc Fe–Co alloys Journal Article Journal of Applied Physics, 108 (2), pp. 023519, 2010. Links | BibTeX | Tags: Fe, phonon, vibrational entropy @article{lucas_effects_2010, title = {Effects of chemical composition and B2 order on phonons in bcc Fe–Co alloys}, author = {M S Lucas and J A Munoz and L Mauger and Chen W Li and A O Sheets and Z Turgut and J Horwath and D L Abernathy and M B Stone and O Delaire and Y Xiao and B Fultz}, url = {http://aip.scitation.org/doi/10.1063/1.3456500}, doi = {10.1063/1.3456500}, year = {2010}, date = {2010-01-01}, journal = {Journal of Applied Physics}, volume = {108}, number = {2}, pages = {023519}, keywords = {Fe, phonon, vibrational entropy}, pubstate = {published}, tppubtype = {article} } |
Li, Chen W; McKerns, M M; Fultz, B A Raman Spectrometry Study of Phonon Anharmonicity of Zirconia at Elevated Temperatures Journal Article Journal of the American Ceramic Society, 94 (1), pp. 224-229, 2010. Abstract | Links | BibTeX | Tags: anharmonicity, high temperature, oxide, phonon, Raman @article{li_raman_2010, title = {A Raman Spectrometry Study of Phonon Anharmonicity of Zirconia at Elevated Temperatures}, author = {Chen W Li and M M McKerns and B Fultz}, url = {http://doi.wiley.com/10.1111/j.1551-2916.2010.04057.x}, doi = {10.1111/j.1551-2916.2010.04057.x}, year = {2010}, date = {2010-01-01}, journal = {Journal of the American Ceramic Society}, volume = {94}, number = {1}, pages = {224-229}, abstract = {Raman spectra of monoclinic zirconia (ZrO2) were measured at temperatures of up to 950 K. Temperature‐dependent Raman peak shifts and broadenings were reported and compared with prior results on hafnia...}, keywords = {anharmonicity, high temperature, oxide, phonon, Raman}, pubstate = {published}, tppubtype = {article} } Raman spectra of monoclinic zirconia (ZrO2) were measured at temperatures of up to 950 K. Temperature‐dependent Raman peak shifts and broadenings were reported and compared with prior results on hafnia... |
Li, Chen W; McKerns, M M; Fultz, B Raman spectrometry study of phonon anharmonicity of hafnia at elevated temperatures Journal Article Physical Review B, 80 (5), pp. 1745, 2009. Abstract | Links | BibTeX | Tags: anharmonicity, high temperature, oxide, phonon, Raman @article{li_raman_2009, title = {Raman spectrometry study of phonon anharmonicity of hafnia at elevated temperatures}, author = {Chen W Li and M M McKerns and B Fultz}, url = {https://link.aps.org/doi/10.1103/PhysRevB.80.054304}, doi = {10.1103/PhysRevB.80.054304}, year = {2009}, date = {2009-08-01}, journal = {Physical Review B}, volume = {80}, number = {5}, pages = {1745}, abstract = {Raman spectra of monoclinic hafnium oxide $(textbackslashtextHfO_2)$ were measured at temperatures up to 1100 K. Raman peak shifts and broadenings are reported. Phonon dynamics calculations were performed with the shell model to obtain the total and partial phonon density of states, and to identify the individual motions of Hf and O atoms in the Raman modes. Correlating these motions to the thermal peak shifts and broadenings, it was found that modes involving changes in oxygen-oxygen bond length were the most anharmonic. The hafnium-dominated modes were more quasiharmonic and showed less broadening with temperature. Comparatively, the oxygen-dominated modes were more influenced by the cubic term in the interatomic potential than the hafnium-dominated modes. An approximately quadratic correlation was found between phonon-line broadening and softening.}, keywords = {anharmonicity, high temperature, oxide, phonon, Raman}, pubstate = {published}, tppubtype = {article} } Raman spectra of monoclinic hafnium oxide $(textbackslashtextHfO_2)$ were measured at temperatures up to 1100 K. Raman peak shifts and broadenings are reported. Phonon dynamics calculations were performed with the shell model to obtain the total and partial phonon density of states, and to identify the individual motions of Hf and O atoms in the Raman modes. Correlating these motions to the thermal peak shifts and broadenings, it was found that modes involving changes in oxygen-oxygen bond length were the most anharmonic. The hafnium-dominated modes were more quasiharmonic and showed less broadening with temperature. Comparatively, the oxygen-dominated modes were more influenced by the cubic term in the interatomic potential than the hafnium-dominated modes. An approximately quadratic correlation was found between phonon-line broadening and softening. |
