title: Ab initio Prediction of Martensitic and Intermartensitic Phase Boundaries in Ni-Mn-Ga.
abstract: Despite the importance of martensitic transformations of Ni-Mn-Ga Heusler alloys for their magnetocaloric and shape-memory properties, the martensitic part of their phase diagrams is not well determined. Using an ab initio approach that includes the interplay of lattice and vibrational degrees of freedom we identify an intermartensitic transformation between a modulated and a nonmodulated phase as a function of excess Ni and Mn content. Based on an evaluation of the theoretical findings and experimental x-ray diffraction data for Mn-rich alloys, we are able to predict the phase diagram for Ni-rich alloys. In contrast to other mechanisms discussed for various material systems in the literature, we herewith show that the intermartensitic transformation can be understood solely using thermodynamic concepts.
authors.affiliation: Max-Planck-Institut für Eisenforschung GmbH, D-40237 Düsseldorf, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Dutta
authors.affiliation: Muğla Üniversitesi, Metalurji ve Malzeme Mühendisliği Bölümü 48000 Muğla, Turkey.
authors.forename: A
authors.initials: A
authors.lastname: Çakır
authors.affiliation: European Synchrotron Research Facility, 38043 Grenoble Cedex 9, France.
authors.forename: C
authors.initials: C
authors.lastname: Giacobbe
authors.affiliation: Max-Planck-Institut für Eisenforschung GmbH, D-40237 Düsseldorf, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Al-Zubi
authors.affiliation: Max-Planck-Institut für Eisenforschung GmbH, D-40237 Düsseldorf, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Hickel
authors.affiliation: Experimentalphysik, Universität Duisburg-Essen, D-47048 Duisburg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Acet
authors.affiliation: Max-Planck-Institut für Eisenforschung GmbH, D-40237 Düsseldorf, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Neugebauer