Regensburg 2013 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 25: Critical Phenomena and Phase Transitions
DY 25.2: Talk
Thursday, March 14, 2013, 09:45–10:00, H46
The role of phonons in the thermodynamics of Fe — •Michael Leitner1,2, Jürgen Neuhaus1,2, Karl Nicolaus1, Winfried Petry1,2, Bernard Hennion3, and Arno Hiess4 — 1Technische Universität München, Physik Department E13, 85747 Garching, Germany — 2Technische Universität München, Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II), 85747 Garching, Germany — 3Laboratoire Léon Brillouin, CEA Saclay, 91191 Gif-sur-Yvette Cédex, France — 4Institut Laue-Langevin, 38042 Grenoble, France, now at European Spallation Source AB, 22100 Lund, Sweden
We report measurements of the phonon dispersions for the three ambient-pressure phases of pure iron (α-Fe, γ-Fe and δ-Fe) by inelastic neutron scattering. Generally, the anharmonic effects lead to a softening of the phonons. Modelling the dispersions by a Born-von Kármán model with temperature-dependent force constants allows us to deduce the vibrational contributions to the energy and entropy differences at the phase transitions. We can conclude that while the latent heats arise mainly from the electronic contributions, the vibrational contributions to the entropy can not be neglected, and especially the γ↔δ-transition is driven mainly by the increased vibrational entropy of the open bcc structure.