Inelastic neutron scattering was used to measure phonon spectra on MgB2 and Mg0.75Al0.25B2 from 7 K 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 parameter and phonon dynamics at elevated temperature in the quasiharmonic approximation. Most of the temperaturedependence of the phonon DOS could be understood with the quasiharmonic approximation, although there was also significant thermal broadening of the phonon spectra. In comparison to Mg0.75Al0.25B2, in the energy range of 60 to 80 meV the experimental phonon spectra from MgB2 showed a non-monotonic change with temperature around 500 K. This may originate from a change with temperature of the adiabatic electron-phonon coupling.2

The phonon densities of states of body-centered-cubic Fe-V alloys across the full composition range were studied by inelastic neutron scattering, nuclear resonant inelastic x-ray scattering, and ab initio calculations. The average phonon energy followed the inverse of the electronic heat capacity and the inverse of the electronic density of states at the Fermi level, showing how the interatomic forces depend on electronic screening. These quantities, including phonon energy, changed rapidly near the composition of the paramagneticferromagnetic transition. For Fe-and V-rich alloys, the thermal phonon softening deviated from quasiharmonic behavior but better agreement was found for intermediate compositions. The Fe partial phonon density of states has a distinctly different shape than V for alloys with less than 50 at. % Fe.