Anomalous phonon damping in the high temperature shape memory alloy Ti50Pd42Cr8

Neutron-scattering measurements of the high temperature shape memory alloy Ti50Pd50-xCrx were performed to probe the phonon precursors to the martensitic transformation. For x=0, the transformation temperature, TM, is ∼800 K[1] and, for the composition studied, x=8%, it is reduced to ∼400 K. Above this temperature the crystal possesses a simple CsCl-type cubic structure. Transverse acoustic phonons propagating along the [ζ ζ 0] direction with atomic displacements along [-ζ ζ 0] were studied at temperatures up to 873 K. The phonons are well defined near the zone center but, for ζ>0.15, they are strongly overdamped near the transition temperature, and become better defined at higher temperatures. An elastic peak develops in the cubic phase at ζ=0.22 and increases in intensity as TM is approached. However, the phonons do not show any characteristic anomaly at this particular ζ.