Phonon modes in Pd-Pt and other substitutional alloys with large mass disorder

Firstly the results of a neutron scattering experiment on the phonon dispersion relations and phonon lifetimes in the alloy Pdsub(0.84)-Ptsub(0.16) are reported and compared with those of an existing coherent-potential approximation calculation. Good agreement is found in the frequency and shape of the resonance and remaining discrepancies are discussed. Then the results of existing or new CPA calculations for several other alloys are compared with experimental data on resonant and localized modes observed by other authors in the alloys. For these other systems in most cases a satisfactory agreement is found in the frequency position and shape of the resonance or of the localized mode, when the alloy characteristics are suited for a straightforward application of mass defect CPA. The relevance of these tests for CPA is also discussed