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Competing tetragonal and monoclinic phases in Ni2.2Mn0.80Ga

Journal of Applied Physics 106(3): -

Autoren/Herausgeber: Ranjan R
Singh S
Boysen H
Trots D
Banik S
Awasthi AM
Mukhopadhyay PK
Barman SR
Erschienen: 2009

Temperature dependent synchrotron x-ray powder diffraction, differential scanning calorimetry, and magnetic measurements were performed on Ni2+xMn1-xGa (x=0.20 and 0.35) magnetic shape memory alloys. For x=0.20, though the monoclinic phase is thermodynamically stable, a trace of residual stress can stabilize a tetragonal phase. The residual-stress-induced tetragonal phase transforms to the cubic austenite phase over an unusually large temperature range (348 K < T < 693 K), suggesting extremely slow kinetics of transformation. In contrast to x=0.20, the thermodynamically stable phase of x=0.35 is tetragonal and this composition exhibits the usual features of a reversible martensitic transformation. The results suggest that for x=0.20 the monoclinic and tetragonal phases are nearly degenerate.