We present a neutron scattering study of the vibrations of a light-atom defect which, in contrast with earlier studies, is both chemically identical to and half the mass of its heavy atom host, namely, 3.7% at. % H β-palladium deuteride. We observe a large shift in hydrogen vibration modes from those in β-PdH, which is in close agreement with the local-mode frequency predicted for an isolated mass defect and provides a prototype example for such a system.

• Received 14 February 1985

DOI:https://doi.org/10.1103/PhysRevB.31.6102