Diffraction features due to ordered distribution of twin boundaries in orthorhombic Ni–Mn–Ga crystals

Ustinov, А.I.; Olikhovska, L.; Glavatska, N.; Glavatskyy, I.

doi:10.1107/s0021889809007171

Cited by 18 publications

(10 citation statements)

References 13 publications

(12 reference statements)

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“…The authors conclude that only a sinusoidal modulation is consistent with the additional diffraction peaks arising from the incommensurate nature of the structure. However, the comparison was made with respect to a simplified model of incommensurate nanotwinning proposed earlier by Ustinov et al () for the description of commensurate structures. It assumes a constant probability of introducing a twin boundary at any given layer beyond a mininum twin width

ℓ

.…”

Section: Microstructure and Msm Effect In Ordered Ni2 Mnga Heusler Comentioning

confidence: 99%

Magnetoelastic coupling and the formation of adaptive martensite in magnetic shape memory alloys

Gruner

Fähler

Entel

2014

Physica Status Solidi (b)

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Reviewing the results of recent first‐principles calculations, we work out a close analogy between the two paradigmatic classes of magnetic shape memory materials, the ordered Ni2 MnGa Heusler compound and the disordered Fe70 Pd30 alloy. Despite fundamental differences between both systems, we can demonstrate that in both cases the very low formation energy for tetragonal twins on the smallest length scale opens an alternative transformation path into an adaptive hierarchical microstructure which is important for the functional behavior. The low energy of the (101) twin boundary corresponds to a shear instability which is associated to the soft transversal acoustic phonon in both systems. In turn, changes of the energy landscape upon magnetic disorder are responsible for the stability of austenite. This points out the strong influence of magnetoelastic coupling on the transformation process. Nanotwinned adaptive microstructures in Ni2 MnGa and Fe68 Pd32 magnetic shape memory alloys obtained from first‐principles calculations.

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ℓ

.…”

Section: Microstructure and Msm Effect In Ordered Ni2 Mnga Heusler Comentioning

confidence: 99%

Magnetoelastic coupling and the formation of adaptive martensite in magnetic shape memory alloys

Gruner

Fähler

Entel

2014

Physica Status Solidi (b)

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“…Previously, Ustinov et al . 37 calculated the peculiar diffraction effects and apparent lattice symmetry resulting from the short range order of adaptive nanotwins in Ni-Mn-Ga. Straka et al . 27 reported experimental observations of a / b nanotwins in a very narrow (<1 K) temperature range in close vicinity of martensitic transformation.…”

Section: Introductionmentioning

confidence: 99%

Low temperature a/b nanotwins in Ni50Mn25+xGa25−x Heusler alloys

Straka¹,

Drahokoupil²,

Veřtát³

et al. 2018

Sci Rep

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We have found low temperature a/b nanotwins having (110) twinning plane in a five-layered modulated martensite phase of Ni50Mn25+xGa25−x (at. %) Heusler alloys and identified the particular region in phase diagram where the nanotwinning occurs. Evolution of the structure with decreasing temperature was studied by X-ray diffraction using single crystals exhibiting magnetic shape memory effect. The merging of (400) and (040) lines upon cooling for 2.6 < x < 3.5 indicated a/b nanotwinning originating from the refinement of initially coarse a/b twins. Refinement of the twins with decreasing temperature was observed directly using scanning electron microscopy. The prerequisite for nanotwinning is an extremely low twin boundary energy, which we estimated using first-principles calculations to be 0.16 meV/Å2. As the nanotwinning distorts the relation between the crystal lattice and the X-ray diffraction pattern, it should be taken into consideration in structural studies of Ni-Mn-Ga Heusler alloys.

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“…The determination of the structure is complicated by deep hierarchical twinning and other lattice imperfections 35 . For example, the 10M monoclinic structure can become apparently tetragonal by the {110} twinning 25 , 36 and also the experimentally determined monoclinic angle can be smaller. To reveal the effect of such twining on the MEP, we also calculated the transformation between austenite and martensitic structure described by the stacking sequence, which represents the 10M martensite with the highest possible density of {110} twin boundaries.…”

Section: Discussionmentioning

confidence: 99%

Transformation Paths from Cubic to Low-Symmetry Structures in Heusler Ni2MnGa Compound

Zelený

Straka

Sozinov

et al. 2018

Sci Rep

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In order to explain the formation of low-temperature phases in stoichiometric Ni2MnGa magnetic shape memory alloy, we investigate the phase transformation paths from cubic austenite with Heusler structure to low-symmetry martensitic structures. We used ab initio calculations combined with the generalized solid state nudged elastic band method to determine the minimum energy path and corresponding changes in crystal lattice. The four-, five-, and seven-layered modulated phases of martensite (4O, 10M, and 14M) are built as the relaxed nanotwinned non-modulated (NM) phase. Despite having a total energy larger than the other martensitic phases, the 10M phase will spontaneously form at 0 K, because there is no energy barrier on the path and the energy decreases with a large negative slope. Moreover, a similar negative slope in the beginning of path is found also for the transformation to the 6M premartensite, which appears as a local minimum on the path leading further to 10M martensite. Transformation paths to other structures exhibit more or less significant barriers in the beginning hindering such a transformation from austenite. These findings correspond to experiment and demonstrates that the kinetics of the transformation is decisive for the selection of the particular low-symmetry structure.

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Diffraction features due to ordered distribution of twin boundaries in orthorhombic Ni–Mn–Ga crystals

Cited by 18 publications

References 13 publications

Magnetoelastic coupling and the formation of adaptive martensite in magnetic shape memory alloys

Magnetoelastic coupling and the formation of adaptive martensite in magnetic shape memory alloys

Low temperature a/b nanotwins in Ni50Mn25+xGa25−x Heusler alloys

Transformation Paths from Cubic to Low-Symmetry Structures in Heusler Ni2MnGa Compound

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