Phonon precursors to the high temperature martensitic transformation in Ti$_{50}$Pd$_{42}$Cr$_8$

S.M. Shapiro; B.L. Winn; D.L. Schlagel; T.A. Lograsso; R.L. Erwin

doi:doi:10.1051/jp4:20031061

Numéro		J. Phys. IV France Volume 112, October 2003


Page(s)		1047 - 1050
DOI		https://doi.org/10.1051/jp4:20031061

J. Phys. IV France 112 (2003) 1047
DOI: 10.1051/jp4:20031061

Phonon precursors to the high temperature martensitic transformation in Ti ₅₀Pd ₄₂Cr ₈

S.M. Shapiro¹, B.L. Winn¹, D.L. Schlagel², T.A. Lograsso² and R.L. Erwin³

¹ Brookhaven National Laboratory, P.O. Box 5000, Upton, NY 11973, U.S.A.
² Ames Laboratory, Ames, IA 50011, U.S.A.
³ National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, U.S.A.

Abstract
Inelastic neutron scattering measurements were carried out on the Ti ₂₀Pd $_{50-\rm x}$ Cr $_{\rm x}$ alloy, which is a high temperature shape memory material. For $\rm x=0$ , the transformation temperature is ~800K and for the composition studied ( $\rm x=8$ at %) M $_{\rm s}\sim 400$ K. The majority of the measurements were performed in the parent, B2-phase, up to 873K. Most of the phonons propagating along the three symmetry directions [ $\zeta$ 00] , [ $\zeta \zeta \zeta$ ] , and [ $\zeta\zeta$ 0] were well defined with the exception of the [ $\zeta\zeta$ 0] transverse acoustic mode with displacements along the [ - $\zeta\zeta$ 0] corresponding to the $\rm C'=l/2 (C_{11}-C_{12}$ ) etastic constant in the $\zeta \to 0$ limit. These phonons are well defined for small $\zeta$ , but for $\zeta > 0.10$ they are strongly overdamped near the transition temperature and become better defined at higher temperatures. An elastic peak develops in the cubic phase at $\zeta =0.22$ and increases in intensity as M $_{\rm s}$ is approached. However, the dispersion curves show no anomaly at this particular wavevector, in marked contrast to the lattice dynamic studies of other systems exhibiting Martensitic transformations.