Anomalous phonon behavior in the high-temperature shape-memory alloy Ti50Pd50â‹TMxCrx

Ti50Pd50−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 andq dependences 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. Disciplines Condensed Matter Physics | Metallurgy Comments This article is from Physical Review B 76 (2007): 054305, doi:10.1103/PhysRevB.76.054305. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ameslab_pubs/78 Anomalous phonon behavior in the high-temperature shape-memory alloy Ti50Pd50−xCrx S. M. Shapiro, Guangyong Xu, and B. L. Winn Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA D. L. Schlagel and T. Lograsso Ames Laboratory and Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA R. Erwin Center for Neutron Research, NIST, 100 Bureau Drive, MS 8562, Gaithersburg, Maryland 20899-8562, USA Received 10 May 2007; published 17 August 2007 Ti50Pd50−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 dependences 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. DOI: 10.1103/PhysRevB.76.054305 PACS number s : 63.20. e, 61.12. q, 62.20.Dc, 64.70.Kb