Elasticity and anharmonicity in iridium

Iridium is a 5-D face-centered-cubic noble metal with exceptional properties, such as a high melting point near 2700 K and exceptional resistance to corrosion. The elastic tensor was known at 10 and 300 K, but only the c 44 temperature depdenced was reported. Likewise, phonon dispersion relations were published only at room temperature. Here, we report temperature-dependent resonant ultrasound spectroscopy data for iridium between 4 and 300 K and phonon dispersion relations between 100 and 700 K. These data reveal normal Varshnii-type elastic behavior and large phonon anharmonicity. Density functional theory calculations and inelastic neutron scattering indicate a Kohn anomaly associated with Fermi-surface nesting. We’ll discuss the behavior of iridium in comparison with neighboring 5-D elements. [Work supported by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. Research conducted at Oak Ridge National Laboratory's (ORNL) neutron sources was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US DOE. Computational resources provided by the National Energy Research Scientific Computing Center (NERSC) and the Compute and Data Environment for Science (CADES) at ORNL, supported by the Office of Science of the U.S. DOE under Contracts No. DE-AC02-05CH11231 and DE-AC05-00OR22725, respectively].