Eur. Phys. J. B 11, 75-81 (1999)
https://doi.org/10.1007/s100510050918

TA_1[110] phonon dispersion and martensitic phase transition in ordered alloys Fe_3Pt

¹ Labor für Tieftemperaturphysik and SFB 166, Gerhard-Mercator-Universität Duisburg, 47048 Duisburg, Germany
² Physik Department E13, Technische Universität München, 85747 Garching, Germany
³ Laboratoire Léon Brillouin, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
⁴ Institut für Experimentalphysik IV and SFB 166, Ruhr Universität Bochum, 44780 Bochum, Germany

Corresponding author: ^a kaestner@ttphysik.uni-duisburg.de

Received: 18 January 1999
Revised: 11 March 1999
Published online: 15 September 1999

Abstract

In a previous neutron scattering study, we had observed that the TA phonon softening in L1₂-ordered ferromagnetic Fe₇₂Pt₂₈ Invar is pronounced at the zone boundary M-point and leads to an antiferrodistortive phase transition at low temperatures. Here, we report on similar neutron scattering investigations on two ordered crystals with higher Fe content to investigate the relation between the TA phonon softening and the martensitic transformation, which occurs in Fe-rich ordered Fe-Pt. We find that the TA phonon softening, especially at the M-point zone boundary, does not depend on the composition of the investigated crystals. In Fe_74.5Pt_25.5, however, the antiferrodistortive phase transition temperature is enhanced due to tetragonal strain preceding the martensitic transition. In Fe₇₇Pt₂₃ a precursor driven premartensitic phase transition is not observed. The structure of the martensite is, however, influenced by the soft mode lattice instability of the austenite. This would explain the origin of structural details found previously for Fe₃Pt thermoelastic martensite.