@article{Sun2023,

title = {Spin-Phonon Interactions Induced Anomalous Thermal Conductivity in Nickel (II) Oxide},

author = {Qiyang Sun and Songrui Hou and Bin Wei and Yaokun Su and Victor Ortiz and Bo Sun and Jiao Y. Y. Lin and Hillary Smith and Sergey Danilkin and Douglas L. Abernathy and Richard B. Wilson and Chen Li},

url = {https://www.sciencedirect.com/science/article/abs/pii/S254252932300130X},

doi = {10.1016/j.mtphys.2023.101094},

year  = {2023},

date = {2023-05-02},

urldate = {2023-05-02},

journal = {Materials Today Physics},

pages = {101094},

abstract = {Nickel (II) oxide is a prominent candidate for spintronic and spin-caloritronic applications operating at room temperature. Although there are extensive studies on nickel oxide, the roles of magnon- and spin-phonon interactions on thermal transport are not well understood. In the present work, the relationship between spin-phonon interactions and thermal transport is investigated by performing inelastic neutron scattering, time-domain thermoreflectance thermal conductivity measurements, and atomistic thermal transport calculations. Inelastic neutron scattering measurements of the magnon lifetime imply that magnon thermal conductivity is trivial, and so heat is conducted only by phonons. Time-domain thermoreflectance measurements of the thermal conductivity vs. temperature follow T-1.5 in the antiferromagnetic phase. This temperature dependence cannot be explained by phonon-isotope and phonon-defect scattering or phonon softening. Instead, we attribute this to magnon-phonon scattering and spin-induced dynamic symmetry breaking. The spin-phonon interactions are saturated in the paramagnetic phase and lead to a weaker temperature dependence of T-1.0 at 550-700 K. These results reveal the importance of spin-phonon interactions on lattice thermal transport, shedding light on the engineering of functional antiferromagnetic spintronic and spin-caloritronic materials through these interactions.},

keywords = {anharmonicity, DFT, lattice dynamics, magnon, magnon-phonon, neutron, oxide, phonon, thermal transport},

pubstate = {published},

tppubtype = {article}

}

@article{Cai2023,

title = {Spin\textendashPhonon Interactions and Anharmonic Lattice Dynamics in Fe3GeTe2},

author = {Qingan Cai and Yuemei Zhang and Diana Luong and Christopher A. Tulk and Boniface P.T. Fokwa and Chen Li},

url = {https://onlinelibrary.wiley.com/doi/10.1002/apxr.202200089},

doi = {10.1002/apxr.202200089},

year  = {2023},

date = {2023-03-24},

urldate = {2023-03-24},

journal = {Advanced Physics Research},

number = {2200089},

abstract = {Raman scattering is performed on Fe3GeTe2 (FGT) at temperatures from 8 to 300 K and under pressures from the ambient pressure to 9.43 GPa. Temperature-dependent and pressure-dependent Raman spectra are reported. The results reveal respective anomalous softening and moderate stiffening of the two Raman active modes as a result of the increase of pressure. The anomalous softening suggests anharmonic phonon dynamics and strong spin\textendashphonon coupling. Pressure-dependent density functional theory and phonon calculations are conducted and used to study the magnetic properties of FGT and assign the observed Raman modes E^2_2g and A^1_1g. The calculations proved the strong spin\textendashphonon coupling for the E^2_2g mode. In addition, a synergistic interplay of pressure-induced reduction of spin exchange interactions and spin\textendashorbit coupling effect accounts for the softening of the E^2_2g mode as pressure increases.},

keywords = {anharmonicity, DFT, high pressure, magnon-phonon, Raman, selenide},

pubstate = {published},

tppubtype = {article}

}

@article{Hou2023,

title = {Response of vibrational properties and thermal conductivity of perovskites to pressure},

author = {Songrui Hou and Richard B. Wilson and Chen Li},

url = {https://www.sciencedirect.com/science/article/pii/S2542529323000469#gs7},

doi = {doi.org/10.1016/j.mtphys.2023.101010},

year  = {2023},

date = {2023-02-10},

journal = {Materials Today Physics},

volume = {32},

number = {101010},

abstract = {We study the response of SrTiO3 and KTaO3's vibrational properties and thermal conductivity to pressurization. Our goal is to improve the understanding of the relationship between crystal structure, vibrational dynamics, and thermal conductivity in perovskites. We measure the thermal conductivity of SrTiO3 and KTaO3 up to 28 GPa by time-domain thermoreflectance. We also perform Raman scattering and stimulated Brillouin scattering measurements of SrTiO3 and KTaO3 to characterize changes in vibrational dynamics with pressure. The thermal conductivity of SrTiO3 increases under pressure with a slope comparable to that of other perovskites whose thermal conductivity has been measured versus pressure. Alternatively, the thermal conductivity of KTaO3 has a stronger pressure dependence than that of other materials with similar crystal structure. We correlate pressure-induced changes in Raman and Brillouin spectra with pressure-induced changes in thermal conductivity. We show that pressure-induced changes in phonon lifetimes dominate the pressure dependence of thermal conductivity. This study provides benchmark knowledge of why Lambda depends on pressure and improves understanding of structure/thermal-property relationships.

},

keywords = {high pressure, phonon, thermal transport},

pubstate = {published},

tppubtype = {article}

}

@article{Cai2022,

title = {Monolayer-like Lattice Dynamics in Bulk WSe2},

author = {Qingan Cai and Bin Wei and Qiyang Sun and Ayman H. Said and Chen Li },

url = {https://www.sciencedirect.com/science/article/pii/S2542529322002541 },

doi = {doi.org/10.1016/j.mtphys.2022.100856},

year  = {2022},

date = {2022-11-01},

urldate = {2022-11-01},

journal = {Materials Today Physics},

volume = {28},

pages = {100856},

abstract = {Understanding the microscopic lattice dynamics is essential for regulating the thermal properties in two-dimensional layered materials. In transition metal dichalcogenides, the layered structures result in different but closely related phonon dispersions between monolayer and bulk. Here, by combining inelastic X-ray scattering and first-principles calculations, the lattice dynamics of tungsten diselenide (WSe2) was investigated comprehensively, and a monolayer-like lattice dynamics in the bulk WSe2 was revealed. We performed the first temperature-dependent phonon dispersions measurement and obtained the mode Gr\"{u}neisen parameters of bulk WSe2, which are found to be in better agreement with the calculations on the monolayer system than those of the bulk. This observation indicates that lattice dynamics in bulk WSe2 hold the characteristic of monolayers. The result provides valuable insights into the thermal properties of WSe2-based devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Haberl2022,

title = {Multi-Extreme Conditions at the Second Target Station},

author = {B. Haberl and D. G. Quirinale and C. Li and G. E. Granroth and H. Nojiri and M.-E. Donnelly and S. V. Ushakov and R. Boehler and B. L. Winn},

url = {https://aip.scitation.org/doi/10.1063/5.0093065},

doi = {10.1063/5.0093065},

year  = {2022},

date = {2022-08-22},

journal = { Review of Scientific Instruments},

volume = {93},

number = {083907},

issue = {8},

abstract = {Three concepts for the application of multi-extreme conditions under in situ neutron scattering are described here. The first concept is a neutron diamond anvil cell made from a non-magnetic alloy. It is shrunk in size to fit existing magnets and future magnet designs and is designed for best pressure stability upon cooling. This will allow for maximum pressures above 10 GPa to be applied simultaneously with (steady-state) high magnetic field and (ultra-)low temperature. Additionally, an implementation of miniature coils for neutron diamond cells is presented for pulsed-field applications. The second concept presents a set-up for laser-heating a neutron diamond cell using a defocused CO2 laser. Cell, anvil, and gasket stability will be achieved through stroboscopic measurements and maximum temperatures of 1500 K are anticipated at pressures to the megabar. The third concept presents a hybrid levitator to enable measurements of solids and liquids at temperatures in excess of 4000 K. This will be accomplished by a combination of bulk induction and surface laser heating and hyperbaric conditions to reduce evaporation rates. The potential for deployment of these multi-extreme environments within this first instrument suite of the Second Target Station is described with a special focus on VERDI, PIONEER, CENTAUR, and CHESS. Furthermore, considerations for deployment on future instruments, such as the one proposed as TITAN, are discussed. Overall, the development of these multi-extremes at the Second Target Station, but also beyond, will be highly advantageous for future experimentation and will give access to parameter space previously not possible for neutron scattering.},

keywords = {extreme environment, high pressure, instrument, neutron scattering},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Thermal Conductivity of BAs under Pressure},

author = {Songrui Hou and Bo Sun and Fei Tian and Qingan Cai and Youming Xu and Shanmin Wang and Xi Chen and Zhifeng Ren and Chen Li and Richard B. Wilson},

url = {https://onlinelibrary.wiley.com/doi/10.1002/aelm.202200017},

doi = {10.1002/aelm.202200017},

year  = {2022},

date = {2022-07-22},

urldate = {2022-07-22},

journal = {Advanced Electronic Materials},

number = {2200017},

abstract = {The thermal conductivity of boron arsenide (BAs) is believed to be influenced by phonon scattering selection rules due to its special phonon dispersion. Compression of BAs leads to significant changes in phonon dispersion, which allows for a test of first principles theories for how phonon dispersion affects three- and four-phonon scattering rates. This study reports the thermal conductivity of BAs from 0 to 30 GPa. Thermal conductivity vs. pressure of BAs is measured by time-domain thermoreflectance with a diamond anvil cell. In stark contrast to what is typical for nonmetallic crystals, BAs is observed to have a pressure independent thermal conductivity below 30 GPa. The thermal conductivity of nonmetallic crystals typically increases upon compression. The unusual pressure independence of BAs's thermal conductivity shows the important relationship between phonon dispersion properties and three- and four-phonon scattering rates.},

keywords = {high pressure, phonon, thermal transport},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Distinct Acoustic and Optical Phonon Dependences on Particle Size, Oxidation, and Temperature in Silicon Nanocrystals},

author = {Shuonan Chen and Devin Colema and Douglas L. Abernathy and Arnab Banerjee and Lorenzo Mangolini and Chen Li},

url = {https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.2c04246},

doi = {10.1021/acs.jpcc.2c04246},

year  = {2022},

date = {2022-07-20},

journal = {Joural of Physical Chemistry C},

volume = {126},

issue = {30},

pages = {12704-12711},

abstract = {Phonon, as a momentum carrier, may play an important role in the photoluminescence of silicon nanocrystals. However, a systematic experimental study on phonon dynamics in spatially confined silicon systems remains limited. We used inelastic neutron scattering to investigate particle size, oxidation, and temperature effects on phonon dynamics of silicon nanocrystals by measuring phonon density of states of 12 and 50 nm silicon nanocrystals with several oxidation levels at different temperatures. We showed that the lattice vibrations of large silicon nanocrystals and bulk silicon are substantially different. We found that transverse acoustic phonon modes have much stronger dependences on particle size, oxidation, and temperature than optical phonon modes. We showed that the changes in phonon dynamics have the largest effect on vibrational entropy and free energy of silicon nanocrystals at intermediate temperatures. Our results shed light on phonon dynamics of silicon-based functional nanomaterials and will facilitate further investigations of electron\textendashphonon interactions in spatially confined silicon systems.},

keywords = {confinement, nanoparticle, neutron scattering, phonon, photonics, silicon},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Mutual spin-phonon driving effects and phonon eigenvector renormalization in nickel (II) oxide},

author = {Qiyang Sun and Bin Wei and Yaokun Su and Hillary Smith and Jiao Y. Y. Lin and Douglas L. Abernathy and Chen Li},

url = {https://www.pnas.org/doi/10.1073/pnas.2120553119},

doi = {10.1073/pnas.2120553119},

year  = {2022},

date = {2022-07-12},

urldate = {2022-07-12},

journal = {Proceedings of the National Academy of Sciences},

volume = {119},

issue = {29},

pages = {e2120553119},

abstract = {The physics of mutual interaction of phonon quasiparticles with electronic spin degrees of freedom, leading to unusual transport phenomena of spin and heat, has been a subject of continuing interests for decades. Despite its pivotal role in transport processes, the effect of spin-phonon coupling on the phonon system, especially acoustic phonon properties, has so far been elusive. By means of inelastic neutron scattering and first-principles calculations, anomalous scattering spectral intensity from acoustic phonons was identified in the exemplary collinear antiferromagnetic nickel (II) oxide, unveiling strong spin-lattice correlations that renormalize the polarization of acoustic phonon. In particular, a clear magnetic scattering signature of the measured neutron scattering intensity from acoustic phonons is demonstrated by its momentum transfer and temperature dependences. The anomalous scattering intensity is successfully modeled with a modified magneto-vibrational scattering cross-section, suggesting the presence of spin precession driven by phonon. The renormalization of phonon eigenvector is indicated by the observed “geometry-forbidden” neutron scattering intensity from transverse acoustic phonon. Importantly, the eigenvector renormalization cannot be explained by magnetostriction but instead, it could result from the coupling between phonon and local magnetization of ions.},

keywords = {anharmonicity, antiferromagnetic, first-principles, magnon, magnon-phonon},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Frustration-induced diffusive scattering anomaly and dimension change in FeGe2},

author = {Yaokun Su and Hillary L. Smith and Matthew B. Stone and Douglas L. Abernathy and Mark D. Lumsden and Carl P. Adams and Chen Li},

url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.024406},

doi = {10.1103/PhysRevB.106.024406},

year  = {2022},

date = {2022-07-11},

urldate = {2022-07-11},

journal = {Physical Review B},

volume = {106},

number = {024406},

abstract = {Magnetic frustration, arising from the competition of exchange interactions, has received great attention because of its relevance to exotic quantum phenomena in materials. In the current work, we report an unusual checkerboard-shaped scattering anomaly in FeGe2, far from the known incommensurate magnetic satellite peaks, by inelastic neutron scattering. More surprisingly, such phenomenon appears as spin dynamics at low temperature, but it becomes prominent above N\'{e}el transition as elastic scattering. A model Hamiltonian that includes an intraplane next-nearest neighbor was proposed and such anomaly is attributed to the near-perfect magnetic frustration and the emergence of unexpected two-dimensional magnetic order in the quasi-one-dimensional FeGe2.},

keywords = {frustration, magnetism, magnon-phonon, neutron, neutron scattering, phonon},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Giant anisotropic in-plane thermal conduction induced by Anomalous phonons in pentagonal PdSe2},

author = {Bin Wei and Junyan Liu and Qingan Cai and Ahmet Alatas and Ayman H. Said and Meihua Hua and ChenLi and Jiawang Hong},

url = {https://www.sciencedirect.com/science/article/pii/S2542529321002601?dgcid=coauthor},

doi = {10.1016/j.mtphys.2021.100599},

year  = {2022},

date = {2022-01-01},

urldate = {2021-12-23},

journal = {Materials Today Physics},

volume = {22},

number = {100599},

abstract = {In two-dimensional materials, different atomic stacking induces anisotropic atomic interactions and phonon dispersions, leading to the anisotropy of in-plane thermal transport. Here, we report an exceptional case in layered pentagonal PdSe2, where the bonds, force constants, and lattice constants are nearly-equal along the in-plane crystallographic axis directions, while the thermal conductivity is surprisingly much greater along b-axis than along a-axis with a ratio up to 1.8. Such strong anisotropy is not only unexpected in in-plane uniform structured materials, but also comparable to the record high in-plane anisotropic thermal conductivity in the nonuniform structured material reported to date (the ratio is ∼2.0 in TiS3). By combining the inelastic X-ray scattering measurement and the first-principles calculations, we attribute such high anisotropy to the low-energy phonons along a-axis, particularly their lower group velocities and “avoided-crossing” behavior. The different buckling structures between a- (zigzag-type) and b-axis (flat-type) are mainly responsible for such unique phonon dynamics properties of PdSe2. This finding helps to discover materials with high anisotropic in-plane thermal conductivity in uniform structures and reveals new physics of anisotropy of in-plane thermal conduction. Due to the unique features in structure and thermal transport properties, PdSe2 may serve as a new platform for designing novel devices to route heat flow precisely at the nanoscale.},

keywords = {anharmonicity, TMD},

pubstate = {published},

tppubtype = {article}

}

@article{Wilson2021,

title = {Interfacial thermal transport in spin caloritronic material systems},

author = {F. Angeles and Q. Sun and V. Ortiz and J. Shi and C. Li and R. B. Wilson},

url = {https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.5.114403},

doi = {10.1103/PhysRevMaterials.5.114403},

year  = {2021},

date = {2021-11-11},

urldate = {2021-11-11},

journal = {Physical Review Materials},

number = {114403},

issue = {5},

abstract = {Interfaces often govern the thermal performance of nanoscale devices and nanostructured materials. As a result, accurate knowledge of thermal interface conductance is necessary to model the temperature response of nanoscale devices or nanostructured materials to heating. Here, we report the thermal boundary conductance between metals and insulators that are commonly used in spin-caloritronic experiments. We use time-domain thermoreflectance to measure the interface conductance between metals such as Au, Pt, Ta, Cu, and Al with garnet and oxide substrates, e.g., NiO, yttrium iron garnet (YIG), thulium iron garnet (TmIG), Cr2O3, and sapphire. We find that, at room temperature, the interface conductance in these types of material systems range from 50 to 300MWm−2K−1. We also measure the interface conductance between Pt and YIG at temperatures between 80 and 350 K. At room temperature, the interface conductance of Pt/YIG is 170MWm−2K−1 and the Kapitza length is ∼40 nm. A Kapitza length of 40 nm means that, in the presence of a steady-state heat current, the temperature drop at the Pt/YIG interface is equal to the temperature drop across a 40-nm-thick layer of YIG. At 80 K, the interface conductance of Pt/YIG is 60MWm−2K−1, corresponding to a Kapitza length of ∼300 nm.},

keywords = {lattice dynamics, thermal transport},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Significant phase-space-driven thermal transport suppression in BC8 silicon},

author = {Junyan Liu and Timothy A. Strobel and Haidong Zhang and Doug Abernathy and Chen Li and Jiawang Hong},

url = {https://www.sciencedirect.com/science/article/pii/S2542529321002273?dgcid=author},

doi = {10.1016/j.mtphys.2021.100566},

year  = {2021},

date = {2021-10-29},

journal = {Materials Today Physics},

volume = {21},

pages = {100566},

abstract = {The BC8 silicon allotrope has a lattice thermal conductivity 1\textendash2 orders of magnitude lower than that of diamond-cubic silicon. In the current work, the phonon density of states, phonon dispersion, and lattice thermal conductivity are investigated by inelastic neutron scattering measurements and first-principles calculations. Flat phonon bands are found to play a critical role in the reduction of lattice thermal conductivity in BC8\textendashSi. Such bands in the low-energy range enhance the phonon scattering between acoustic and low-energy optical phonons, while bands in the intermediate-energy range act as a scattering bridge between the high- and low-energy optical phonons. They significantly enlarge the phonon-phonon scattering phase space and reduces the lattice thermal conductivity in this novel silicon allotrope. This work provides insights into the significant reduction of the lattice thermal conductivity in BC8\textendashSi, thus expanding the understanding of novel silicon allotropes and their development for electronic devices.},

keywords = {anharmonicity, lattice dynamics, phonon, thermal transport},

pubstate = {published},

tppubtype = {article}

}

@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 and

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 = {2021-10-12},

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}

}

@article{Hong2021,

title = {Phonon anharmonicity: a pertinent review of recent progress and perspective},

author = {B. Wei and Q. Sun and C. Li and J. Hong},

url = {https://link.springer.com/article/10.1007/s11433-021-1748-7},

doi = {10.1007/s11433-021-1748-7},

year  = {2021},

date = {2021-09-28},

urldate = {2021-07-01},

journal = {SCIENCE CHINA Physics, Mechanics \& Astronomy},

volume = {64},

number = {117001},

keywords = {anharmonicity, lifetime, metal-insulator transition, neutron scattering, thermal transport, vibrational entropy},

pubstate = {published},

tppubtype = {article}

}

@article{Cai2021,

title = {Pressure- and temperature-dependent inelastic neutron scattering study of the phase transition and phonon lattice dynamics in para-terphenyl},

author = {Qingan Cai and Michael McIntire and Luke L. Daemen and Chen Li and Eric L. Chronister},

url = {https://pubs.rsc.org/en/content/articlelanding/2021/cp/d1cp00190f#!divAbstract},

doi = {10.1039/D1CP00190F},

year  = {2021},

date = {2021-03-24},

journal = {Physical Chemistry Chemical Physics},

volume = {23},

pages = {8792},

abstract = {Inelastic neutron scattering has been performed on para-terphenyl at temperatures from 10 to 200 K and under pressures from the ambient pressure to 1.51 kbar. The temperature dependence of phonons, especially low-frequency librational bands, indicates strong anharmonic phonon dynamics. The pressure- and temperature-dependence of the phonon modes suggest a lack of phase transition in the region of 0\textendash1.51 kbar and 10\textendash30 K. Additionally, the overall lattice dynamics remains similar up to 200 K under the ambient pressure. The results suggest that the boundary between the ordered triclinic phase and the third solid phase, reported at lower temperatures and higher pressures, is out of the pressure and temperature range of this study.},

keywords = {high pressure, phonon, Raman},

pubstate = {published},

tppubtype = {article}

}

@article{Li2020b,

title = {Observation of Magnon Polarons in a Uniaxial Antiferromagnetic Insulator},

author = {Junxue Li and Haakon T. Simensen and Derek Reitz and Qiyang Sun and Wei Yuan and Chen Li and Yaroslav Tserkovnyak and Arne Brataas and Jing Shi},

url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.217201},

doi = {10.1103/PhysRevLett.125.217201},

year  = {2020},

date = {2020-11-17},

journal = {Phys. Rev. Lett. },

volume = {125},

pages = {217201},

abstract = {Magnon polarons, a type of hybridized excitations between magnons and phonons, were first reported in yttrium iron garnet as anomalies in the spin Seebeck effect responses. Here, we report an observation of antiferromagnetic (AFM) magnon polarons in a uniaxial AFM insulator Cr2O3. Despite the relatively higher energy of magnon than that of the acoustic phonons, near the spin-flop transition of ∼6T, the left-handed magnon spectrum shifts downward to hybridize with the acoustic phonons to form AFM magnon polarons, which can also be probed by the spin Seebeck effect. The spin Seebeck signal is founded to be enhanced due to the magnon polarons at low temperatures.},

keywords = {antiferromagnetic, magnon, magnon-phonon, polaron},

pubstate = {published},

tppubtype = {article}

}

@article{Fultz2020,

title = {Temperature-dependent phonon lifetimes and thermal conductivity of silicon by inelastic neutron scattering and ab initio calculations},

author = {D. S. Kim and O. Hellman and N. Shulumba and C. N. Saunders and J. Y. Y. Lin and H. L. Smith and J. E. Herriman and J. L. Niedziela and D. L. Abernathy and C. W. Li and B. Fultz},

url = {https://doi.org/10.1103/PhysRevB.102.174311},

doi = {10.1103/PhysRevB.102.174311},

year  = {2020},

date = {2020-11-16},

journal = {Phys. Rev. B},

volume = {102},

pages = {174311},

abstract = {Inelastic neutron scattering on a single crystal of silicon was performed at temperatures from 100 to 1500 K. These experimental data were reduced to obtain phonon spectral intensity at all wave vectors Q and frequencies ω in the first Brillouin zone. Thermal broadenings of the phonon peaks were obtained by fitting and by calculating with an iterative ab initio method that uses thermal atom displacements on an ensemble of superlattices. Agreement between the calculated and experimental broadenings was good, with possible discrepancies at the highest temperatures. Distributions of phonon widths versus phonon energy had similar shapes for computation and experiment. These distributions grew with temperature but maintained similar shapes. Parameters from the ab initio calculations were used to obtain the thermal conductivity from the Boltzmann transport equation, which was in good agreement with experimental data. Despite the high group velocities of longitudinal acoustic phonons, their shorter lifetimes reduced their contribution to the thermal conductivity, which was dominated by transverse acoustic modes.},

keywords = {lattice, lifetime, phonon},

pubstate = {published},

tppubtype = {article}

}

@article{Delaire2020,

title = {Controlling phonon lifetimes via sublattice disordering in AgBiSe2},

author = {J. L. Niedziela and D. Bansal and J. Ding and T. Lanigan-Atkins and Chen Li and A. F. May and H. Wang and J. Y. Y. Lin and D. L. Abernathy and G. Ehlers and A. Huq and D. Parshall and J. W. Lynn and O. Delaire},

url = {https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.4.105402},

doi = {10.1103/PhysRevMaterials.4.105402},

year  = {2020},

date = {2020-08-04},

journal = {Phys. Rev. Materials},

volume = {4},

pages = {105402},

abstract = {Understanding and controlling microscopic heat transfer mechanisms in solids is critical to material design in numerous technological applications. Yet, the current understanding of thermal transport in semiconductors and insulators is limited by the difficulty in directly measuring individual phonon lifetimes and mean free paths, and studying their dependence on the microscopic state of the material. Here we report our measurements of microscopic phonon scattering rates in AgBiSe2, which exhibits a controllable, reversible change directly linked to microstructure evolution near a reversible structural phase transition, that directly impacts the thermal conductivity. We demonstrate a steplike doubling of phonon scattering rates resultant from the cation disordering at the structural transition. To rationalize the neutron scattering data, we leverage a stepwise approach to account for alterations to the thermal conductivity that are imparted by distinct scattering mechanisms. These results highlight the potential of tunable microstructures housed in a stable crystal matrix to provide a practical route to tailor phonon scattering to optimize thermal transport properties.},

keywords = {lattice dynamics, phonon, thermal transport},

pubstate = {published},

tppubtype = {article}

}

@article{Li2020,

title = {Giant low-temperature anharmonicity in silicon nanocrystals},

author = {Shuonan Chen and Devin Coleman and Douglas L. Abernathy and Arnab Banerjee and Luke L. Daemen and Lorenzo Mangolini and Chen W. Li},

url = {https://journals.aps.org/prmaterials/pdf/10.1103/PhysRevMaterials.4.056001},

doi = {10.1103/PhysRevMaterials.4.056001},

year  = {2020},

date = {2020-05-04},

journal = {Phys. Rev. Materials},

volume = {4},

pages = {056001},

abstract = {The phonon density of states of silicon nanocrystals with size between 4 and 7.5 nm was measured by inelastic neutron scattering in the 5-600 K temperature range. The narrow particle size distributions enable the study of size effects on phonon dynamics. Giant softening of phonon features below 30 meV, universal broadening of phonon features, and the disappearance of intermediate-energy phonons were observed with decreasing nanocrystals size. Such size effects are mostly attributed to the structure variations within the nanocrystals. The phonons below 30 meV in silicon nanocrystals show temperature dependence opposite to the bulk silicon, explained by the large anharmonicity of the under-constrained near-surface phonons. This is supported by the abnormal atomic mean-square-displacement, and low energy phonon population in small silicon nanocrystals. This work provides crucial information on the phonon dynamics in spatially confined materials.},

keywords = {anharmonicity, high temperature, lifetime, neutron},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@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}

}

@article{Li2018,

title = {Probing the electrolyte infiltration behaviour of activated carbon supercapacitor electrodes by in situ neutron scattering using aqueous NaCl as electrolyte},

author = {Yiqun Li and Chen W. Li and Cong Li and Yan Chen and Ke An and Kai Landskron},

url = {https://www.sciencedirect.com/science/article/pii/S0008622318304330?via%3Dihub},

doi = {10.1016/j.carbon.2018.04.072},

year  = {2018},

date = {2018-04-24},

journal = {Carbon},

volume = {136},

pages = {139},

abstract = {In situcontrast-matched neutron scattering was used to probe the electrolyte infiltration behavior ofactivated supercapacitor carbon electrodes using an aquoeus 1 M NaCl solution. It was found that onlyabout 20% of the pore volume was infiltrated at chemical equilibrium. The partial infiltration can beattributed to the co-existence of hydrophilic and hydrophilic pores. The study suggests that for theachievement of optimal capacitance, supercapacitor electrodes should be evacuated before electrolyteinfiltration.},

keywords = {carbon, electrolyte, neutron scattering, super capacitor},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@article{Haberl2017b,

title = {Wide-angle diamond cell for neutron scattering},

author = {Bianca Haberl and Sachith Dissanayake and Feng Ye and Luke L. Daemen and Yongqiang Cheng and Chen W. Li and A.-J. Ramirez-Cuesta and Masaaki Matsuda and Jamie J. Molaison and Reinhard Boehler},

url = {https://www.tandfonline.com/doi/full/10.1080/08957959.2017.1390571},

doi = {10.1080/08957959.2017.1390571},

year  = {2017},

date = {2017-10-19},

journal = {High Pressure Research},

volume = {37},

number = {4},

pages = {495-506},

abstract = {A new diamond cell with extreme apertures is described. It is tailored for a large variety of neutron scattering techniques such as inelastic neutron scattering and single-crystal diffraction both at the Spallation Neutron Source (SNS) and the High Flux Isotope Reactor at the Oak Ridge National Laboratory. Simple springs enable forces of over 10 metric tons to be clamped in for low-temperature measurements. At present, low-cost polycrystalline diamond (Versimax) pressure anvils are used. We predict a routine pressure regime up to 20 GPa with sample volumes of ∼0.5 mm3. Future use of large CVD single-crystal diamond anvils will significantly expand this pressure range. We show examples for measurements at the SNAP, VISION and CORELLI beamlines of the SNS.},

keywords = {diamond anvil cell, diffraction, high pressure, neutron scattering},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@article{Li:2015gf,

title = {Orbitally driven giant phonon anharmonicity in~SnSe},

author = {Chen W Li and J Hong and A F May and D Bansal and S Chi and T Hong and G Ehlers and O Delaire},

url = {http://www.nature.com/doifinder/10.1038/nphys3492},

doi = {10.1038/nphys3492},

year  = {2015},

date = {2015-01-01},

journal = {Nature Physics},

volume = {11},

number = {12},

pages = {1063--1069},

keywords = {anharmonicity, neutron, selenide, thermoelectric},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@article{munoz_positive_2011,

title = {Positive Vibrational Entropy of Chemical Ordering in FeV},

author = {J A Munoz and M S Lucas and O Delaire and M L Winterrose and L Mauger and Chen W Li and A O Sheets and M B Stone and D L Abernathy and Y Xiao and P Chow and B Fultz},

url = {https://link.aps.org/doi/10.1103/PhysRevLett.107.115501},

doi = {10.1103/PhysRevLett.107.115501},

year  = {2011},

date = {2011-09-01},

journal = {Physical Review Letters},

volume = {107},

number = {11},

pages = {115501},

keywords = {Fe, neutron, synchrotron, vibrational entropy},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@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}

}

@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}

}

@article{keith_atomsim:_2010,

title = {AtomSim: web-deployed atomistic dynamics simulator},

author = {J B Keith and J R Fennick and D R Nelson and C E Junkermeier and J Y Y Lin and Chen W Li and M M McKerns and J P Lewis and B Fultz},

url = {http://scripts.iucr.org/cgi-bin/paper?S0021889810037209},

doi = {10.1107/S0021889810037209},

year  = {2010},

date = {2010-11-01},

journal = {Journal of Applied Crystallography},

volume = {43},

number = {6},

pages = {1553-1559},

abstract = {AtomSim, a collection of interfaces for computational crystallography simulations, has been developed. It uses forcefield-based dynamics through physics engines such as the General Utility Lattice Program, and can be integrated into larger computational frameworks such as the Virtual Neutron Facility for processing its dynamics into scattering functions, dynamical functions etc. It is also available as a Google App Engine-hosted web-deployed interface. Examples of a quartz molecular dynamics run and a hafnium dioxide phonon calculation are presented.},

keywords = {lattice dynamics, software},

pubstate = {published},

tppubtype = {article}

}

@article{lucas_effects_2010,

title = {Effects of chemical composition and B2 order on phonons in bcc Fe\textendashCo 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}

}

@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}

}

@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}

}

@article{wang_magnetic_2003,

title = {Magnetic levitation force between a superconducting bulk magnet and a permanent magnet},

author = {J J Wang and C Y He and L F Meng and Chen W Li and R S Han and Z X Gao},

url = {http://stacks.iop.org/0953-2048/16/i=4/a=318?key=crossref.0a7e9e017f64b32c5837fc10760d380f},

doi = {10.1088/0953-2048/16/4/318},

year  = {2003},

date = {2003-01-01},

journal = {Superconductor Science and Technology},

volume = {16},

number = {4},

pages = {527-533},

keywords = {magnetism, superconductor},

pubstate = {published},

tppubtype = {article}

}