Commensurate and incommensurate “5M” modulated crystal structures in Ni–Mn–Ga martensitic phases

Righi, Lara; Albertini, F.; Pareti, L.; Paoluzi, A.; Calestani, G.

doi:10.1016/j.actamat.2007.05.040

Cited by 163 publications

(106 citation statements)

References 24 publications

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“…The obtained results of satellite positions of the X-and M-phases are summarized in Fig. 4 together with those of the I-phase under zero stress reported in the previous paper [12]. In the followings, we will discuss the structural relation between the X-phase and the other phases by referring Fig.…”

Section: Discussionmentioning

confidence: 96%

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Structural Relation between the X-Phase and other Phases in Ni<sub>2</sub>MnGa

Kakeshita

Fukuda

Terai

et al. 2009

MSF

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Abstract. We have investigated stress and temperature dependences of the structure of the X-phase in Ni 2 MnGa to understand structural relation between the X-phase and other phases. Position and intensity of satellites of the X-phase are different from those of the intermediate (I-) phase under compressive stress, but they approach those of the I-phase with decreasing stress. That is, the structure change associated with the I → X transformation is discontinuous under a compressive stress, while it is continuous under zero stress. In addition, the transformation from the X-phase to the L2 1 -type parent phase is continuous regardless of applied stress. These results strongly suggest the existence of multi-critical point in Ni 2 MnGa. On the other hand, the transformation from the X-phase to the martensite phase is discontinuous regardless of applied stress.

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Section: Discussionmentioning

confidence: 96%

“…Crystal structures of the M-and I-phases have been intensively investigated so far [7 -10], and recent studies suggest that they have incommensurate structures [12,13]. Moreover, the X-phase also has an incommensurate structure according to our previous study [14].…”

Section: Introductionmentioning

confidence: 99%

Structural Relation between the X-Phase and other Phases in Ni<sub>2</sub>MnGa

Kakeshita

Fukuda

Terai

et al. 2009

MSF

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“…Further structural investigations have demonstrated that the commensurate form of martensitic 5M modulation occurs in off-stoichiometric Ni-Mn-Ga alloys [14]. In particular a polycrystalline sample of composition Ni 2 Mn 1.15 Ga 0.85 has been studied by X-ray powder diffraction at room temperature.…”

Section: Figmentioning

confidence: 99%

“…The modulation function assumed refined parameters very similar to those found for Ni 2 MnGa but the periodicity is actually five-fold commensurate. From the superspace description of the modulated crystal, a classical 3-dimensional structure is straightforwardly obtained (for details see ref [14]). In this case, the advantages provided by the superspace approach appears more evident.…”

Section: Figmentioning

confidence: 99%

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Incommensurate and Commensurate Structural Modulation in Martensitic Phases of FSMA

Righi

Albertini

Paoluzi

et al. 2009

MSF

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Abstract. Magnetic and structural properties in multifunctional FSMA (Ferromagnetic Shape Memory Alloys) belonging to Heusler family are frequently related to the occurrence of structural modulation in martensitic phases. The highest MFIS (Magnetic Field Induced Strain) effect has been observed in Ni-Mn-Ga alloys showing martensitic modulated structures. Depending on the composition, pressure and temperature conditions, this periodic structural distortion, consisting of shuffling of atomic layers along specific crystallographic directions, accompanies the martensitic transformation. Over the years, different modulated martensitic structures have been observed and classified depending upon the periodicity of corresponding superstructure (nM with n=3, 5, 6, 7, 12 etc). On the other hand, it has been demonstrated that in most cases such structural modulation is incommensurate and the crystal structure can be solved by applying superspace approach. The crystallographic representation of different modulated structures, obtained by structure refinement on powder diffraction data, suggests a unified description where every different "nM" periodicity can be straightforwardly represented. It will be presented an overview illustrating structural features of several displacive modulated martensitic lattices. For a specific Ni-Mn-Ga composition, the evolution of structural modulation upon temperature change will be illustrated.

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Reversible Magnetic Field Induced Strain in Ni₂MnGa‐Polymer‐Composites

et al. 2011

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Magnetic shape memory (MSM) alloys are a new class of materials for sensor and actuator applications. Ni-Mn-Ga single crystals show large magnetic-field induced strain (MFIS) in moderate magnetic fields below 1 T caused by reorientation of martensitic variants by twin boundary motion. The maximum possible strain e ¼ 1-(c/a) is given by the lattice parameters a and c of the martensite unit cell resulting in e ¼ 6% for 5M martensite and e ¼ 11% for 7M martensite. [1][2][3] However, the main disadvantage of single crystals is their high brittleness. One possible solution is the synthesis of textured polycrystalline Ni-Mn-Ga for which a MFIS of 1% has been reported. [4] Due to constraints by grain boundaries, the twinning stress s twin for moving twin boundaries is still much higher for polycrystals (s twin > 15 MPa) compared to that in single crystals (s twin < 2 MPa). A strong texture, large grains and a mechanical training can decrease s twin . [4,5] The main disadvantage of single-and polycrystals is their complex preparation.An alternative to single-and polycrystals are Ni-Mn-Ga polymer composites. [6][7][8] Single crystalline particles embedded in a stiffness-matched polymer matrix allow overcoming the disadvantages. A thin polymer film between the single crystalline particles allows the particles to strain und reduces s twin . Another advantage of composites is the decrease of eddy currents due to a non-conducting polymer matrix, which enables high frequency applications, and the simple preparation of textured bulk materials.In previous works, we showed that melt-extracted and subsequently annealed fibres exhibit a bamboo-like grain structure and an MFIS of 1%. [6] However, only small amount of grains in the fibre are active. Different crystallographic orientations of grains as well as still existing grain boundaries hinder activation of the whole fibre. A separation of fibres into nearly single crystalline particles by breaking them alongComposite materials consisting of magnetic shape memory alloy particles and a polymer matrix combine the advantages of both material classes: the high achievable magnetic field induced strain (MFIS) of 6% of Ni-Mn-Ga with a ductile matrix. Engineering the particle-matrix interface as well as matching stiffness of polymer matrix is of importance for achieving high reversible MFIS to use this material as actuator or damper. We investigated those properties for Ni 50.9 Mn 27.1 Ga 22.0 and Ni 50.3 Mn 24.6 Ga 25.1 polymer composites. Particles were produced by gently crushing melt-extracted and subsequently annealed fibres. At room temperature, the Ni 50.9 Mn 27.1 Ga 22.0 particles exhibit a 5M martensitic structure, while the Ni 50.3 Mn 24.6 Ga 25.1 particles are austenitic. These particles were embedded into the polymer, either a stiff epoxy resin or a soft polyurethane. In response to an external applied magnetic field, the particles tend to relocate within the polyurethane due to its very low Young's modulus and magnetostatic interaction between particles. Slightly stiffer pol...

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Commensurate and incommensurate “5M” modulated crystal structures in Ni–Mn–Ga martensitic phases

Cited by 163 publications

References 24 publications

Structural Relation between the X-Phase and other Phases in Ni<sub>2</sub>MnGa

Structural Relation between the X-Phase and other Phases in Ni<sub>2</sub>MnGa

Incommensurate and Commensurate Structural Modulation in Martensitic Phases of FSMA

Reversible Magnetic Field Induced Strain in Ni₂MnGa‐Polymer‐Composites

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Commensurate and incommensurate “5M” modulated crystal structures in Ni–Mn–Ga martensitic phases

Cited by 163 publications

References 24 publications

Structural Relation between the X-Phase and other Phases in Ni<sub>2</sub>MnGa

Structural Relation between the X-Phase and other Phases in Ni<sub>2</sub>MnGa

Incommensurate and Commensurate Structural Modulation in Martensitic Phases of FSMA

Reversible Magnetic Field Induced Strain in Ni2MnGa‐Polymer‐Composites

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Reversible Magnetic Field Induced Strain in Ni₂MnGa‐Polymer‐Composites