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First-principles investigations of the five-layer modulated martensitic structure in Ni(2)Mn(Al(x)Ga(1-x)) alloys
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2011 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, no 15, 5938-5945 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, the five-layer modulated (5M) martensitic structures of Ni(2)Mn(Al(x)Ga(1-x)), with x = 0, 0.1 and 0.2, are investigated by the use of the exact muffin-tin orbital method in combination with the coherent potential approximation. The 5M martensite is modeled by varying c/a (shear) and wave-like displacements of the atoms on (1 1 0) plane (shuffle) scaled by eta according to Martynov and Kokorin (J. Phys. III 2, 739 (1992)). For Ni(2)MnGa, we obtain 5M martensite with equilibrium c/a of 0.92 and eta of 0.08, in reasonable agreement with the experiment results (0.94 and 0.06, respectively). c/a and eta are linearly coupled to each other. Al-doping increases c/a and decreases eta, but the linear c/a similar to eta coupling remains. Comparing the total energies of the 5M martensite and L2(1) austenite, we find that the martensite is more stable than the austenite. Al-doping increases the relative stability of the austenite and finally becomes energetically degenerated with the 5M martensite at an Al atomic fraction (x) of about 0.26. The relative phase stability is analyzed based on the calculated density of states. The calculated total magnetic moments mu(0) as a function of c/a exhibit a maximum around the equilibrium c/a. Al-doping reduces mu(0)

Place, publisher, year, edition, pages
2011. Vol. 59, no 15, 5938-5945 p.
Keyword [en]
Heusler alloy, First-principles calculations, Modulated structure, Martensitic transformation, Shape memory alloys (SMA)
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-158572DOI: 10.1016/j.actamat.2011.06.002ISI: 000294086900007OAI: oai:DiVA.org:uu-158572DiVA: diva2:440537
Available from: 2011-09-13 Created: 2011-09-12 Last updated: 2012-04-02Bibliographically approved

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Johansson, BörjeVitos, Levente
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