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Temperature-dependent lattice dynamics in iridium

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Physical Review Materials
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The characterization of simple elemental systems is key to benchmarking first-principles modeling of electronic and vibrational behaviors of materials. A large body of literature has been built for most elemental systems in the periodic table. However, surprisingly little neutron work has been performed to probe the vibrational properties of iridium, likely due to its large neutron absorption cross section. Nonetheless, iridium is of significant scientific and technological interest due to large relativistic electron effects and electron-phonon coupling, particularly in strongly correlated iridate compounds. Here, we report temperature dependent inelastic neutron scattering measurements of the vibrational properties of iridium, from which we extract key thermodynamic properties. To overcome the challenge of the large neutron absorption of iridium, we developed a novel yet simple post-processing correction procedure. The measured densities of phonon states compare well with quasiharmonic density functional theory calculations, although the obtained experimental phonon Grüneisen parameters are much larger than expected, reaching as high as γ = 4.5, indicating substantial anharmonicity.