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

TL;DR

This study investigates the unusual phonon behavior in TiPd:Cr high temperature shape memory alloys, revealing anomalous temperature-dependent phonon linewidths and dynamics that challenge conventional anharmonic expectations.

Contribution

It provides new insights into the phonon dynamics and lattice behavior of TiPd:Cr alloys, combining experimental diffuse scattering measurements with first principles calculations.

Findings

Broad phonon linewidths across the Brillouin zone

Increase in linewidth with decreasing temperature

No observed anomaly at the premartensitic wave vector q0

Abstract

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