TEM study of pseudo-twin in an off-stoichiometric Ni2MnGa

Abstract We have investigated twin-like microstructure of the martensite phase in a Ni 55.5 Mn 20.0 Ga 24.5 (at.%) alloy by using transmission electron microscope (TEM). The bright field image of the martensite phase showed striped microstructure composed of two crystals. Assuming that both crystals have orthorhombic structures, we calculated the axial ratios c / a and b / a from the 1 1 1 diffraction patterns by using angles between reflections. As a result, we found that the axial ratios of one crystal are slightly different from those of the other crystal. This result implies that the twin-like (striped) microstructure of Ni 55.5 Mn 20.0 Ga 24.5 is not true twin but is pseudo-twin.