Electron Concentration and Structural Transformation of Ni_2MnGa-Based Shape Memory Alloys
In shape memory Ni<SUB>2</SUB>MnGa based alloys, the structural transition temperature (<I>T<SUB>t</SUB></I>) increases with increasing valence electron concentration per atom (<I>e</I>⁄<I>a</I>). That is, when Ni or Mn atoms in Ni<SUB>2</SUB>MnGa are replaced with a fourth element (X atom), the <I>T<SUB>t</SUB></I> increases with increasing atomic number of the X atom. To examine the experimental results, the electronic structures of these alloys were calculated for the cubic and monoclinic structures. The difference <I>ΔE</I> of total energies between the two structures was also calculated as a function of <I>e</I>⁄<I>a</I>. It was found that the features of <I>T<SUB>t</SUB></I> (<I>e</I>⁄<I>a</I>) are similar to those of <I>ΔE</I> (<I>e</I>⁄<I>a</I>). Their features are different in the lower and higher ranges than the boundary <I>e</I>⁄<I>a</I>=7.625. The two features are characterized by two cases: a case that X atoms occupies Ni sites and the other case that X atoms occupy Mn sites. The characteristics mainly come from the difference of the density of states of X atoms at Ni and Mn sites.
- Materials transactions
Materials transactions 43(5), 846-851, 2002-05-01