Influence of atomic order on TA1[110] phonon softening and displacive phase transition in Fe72Pt28 Invar alloys

J. Kästner, W. Petry, S. M. Shapiro, A. Zheludev, J. Neuhaus, Th Roessel, E. F. Wassermann, H. Bach

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16 Scopus citations

Abstract

The acoustic phonon dispersions of two Invar crystals Fe72Pt28, one ordered with the L12 (Cu3Au) structure, the other disordered fcc, have been investigated between 3.4 K and 470 K by inelastic and elastic neutron scattering. For the ordered crystal, pronounced softening of the whole TA1[ξξ0] phonon branch is observed on cooling below the Curie temperature. Particularly strong phonon softening at the M-point zone boundary of the L12 structure leads to a displace, antiferrodistortive Phase transition at low temperatures. For the disordered crystal, much weaker softening of the TA1 [ξξ0] phonons is observed and restricted to the region near the Brillouin zone center, where increasing elastic scattering with decreasing temperature indicates the growth of local tetragonal strain. This strain is considered as a typical precursor of the transformation to bet martensite. Specific heat measurements, performed at low temperatures on both crystals confirm the neutron scattering results and reveal considerable enhancement of the low energy phonon density of states in the ordered crystal.

Original languageEnglish
Pages (from-to)641-648
Number of pages8
JournalEuropean Physical Journal B
Volume10
Issue number4
DOIs
StatePublished - 2 Aug 1999

Keywords

  • 63.20.Dj Phonon states and bands, normal modes, and phonon dispersion
  • 64.70.Kb Solid-solid transitions
  • 65.40.+g Heat capacities of solids

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