Lattice Dynamics of LaFeAsO1-xFx and PrFeAsO1-y via Inelastic X-Ray Scattering and First-Principles Calculation

The lattice dynamics of LaFeAsO1-xFx (x = 0, 0.1) and PrFeAsO1-y (y similar to 0.1) are investigated using inelastic x-ray scattering and ab-initio calculation. Measurements of powder samples provide an approximation to the phonon DOS, while dispersion is measured from a single crystal of PrFeAsO1-y. A model that agrees reasonably well with all of the data at room temperature is built from results of ab-initio calculations by reducing the strength of the Fe-As bond by 30%.