Diffraction effects due to modulation of orthorhombic crystals by aperiodically arranged twin boundaries

The relation between lattice parameters and very low twinning stress in Ni50Mn25+xGa25−xmagnetic shape memory alloys

“…The temperature dependences of lattice parameters a, b, c, and γ were determined for Ni 50 Mn 25+x Ga 25−x single crystals with 10M structure exhibiting very low twinning stress and magnetically induced reorientation (MIR). With decreasing temperature, the lattice parameters a and monoclinic angle γ increased, c decreased, while b was nearly constant.…”

“…Recently Ge et al [49] demonstrated gradual change of lattice parameters resulting from the coarsening of nanotwins during the 14M→NM transformation observed by TEM. All the mentioned effects can significantly influence the diffraction pattern and can result in an additional or missing diffraction peaks and consequent difficulties in lattice symmetry determination [50,51]. In this respect it is also interesting to note that according to Righi et al [52], the transformation of the 10M structure from commensurate to incommensurate did not result in sudden changes in a, b lattice constants.…”

“…Five Ni 50 Mn 25+x Ga 25−x alloys for the study, where x was between 2.7 and 3.9 at.%, Table 1, were produced by directional solidification in Adaptamat Ltd. The alloys were essentially the same as in our previous reports on the twinning stress [14,22].…”

“…The Ni-Mn-Ga based MSMAs with five-layered (10M) martensite structure demonstrate very low twinning stress, especially for the composition Ni 50 Mn 25+x Ga 25−x , where x =2.7-3.9 [10,14]. The very low twinning stress of the order of 0.1 MPa or even 0.01 MPa [15] is observed with Type 2 martensite twin boundaries [16,17,18,19,20] in a broad temperature interval including room temperature [14,21].…”

Thermally induced changes of structure in Ni$_{50}$Mn$_{25+x}$Ga$_{25-x}$ magnetic shape memory single crystals with very low twinning stress

“…Recently Ge et al [49] demonstrated gradual change of lattice parameters resulting from the coarsening of nanotwins during the 14M→NM transformation observed by TEM. All the mentioned effects can significantly influence the diffraction pattern and can result in an additional or missing diffraction peaks and consequent difficulties in lattice symmetry determination [50,51].…”