Anomalous phonon behavior in the high temperature shape memory alloy: TiPd:Cr

摘要

Ti50 Pd50-xCrx is a high temperature shape memory alloy with a martensitictransformation temperature strongly dependent on the Cr composition. Prior tothe transformation a premartensitic phase is present with an incommensuratemodulated cubic lattice with wave vector of q0=(0.22, 0.22, 0). The temperaturedependence of the diffuse scattering in the cubic phase is measured as afunction temperature for x=6.5, 8.5, and 10 at. %. The lattice dynamics hasbeen studied and reveals anomalous temperature and q-dependence of the[110]-TA2 transverse phonon branch. The phonon linewidth is broad over theentire Brillouin zone and increases with decreasing temperature, contrary tothe behavior expected for anharmonicity. No anomaly is observed at q0. Theresults are compared with first principles calculation of the phonon structure.