Role of local structural distortions in the variation of martensitic transformation temperature with / ratio in NiMnZ (Z = In, Sn or Sb) alloys.

NiMnZ (Z = In, Sn or Sb) undergo martensitic transformation with transformation temperature () scaling with the average valence electron per atom (/) ratio. However, the rate of increase of depends on the type of Z atom, with the slope of / curve increasing from Z = In to Z = Sb. Local structural distortions are believed to be the leading cause of martensitic transformation in these alloys. A careful study of the Ni and Mn local structures in several NiMnZ alloys with varying / ratio and the same Z atom, with the same / ratio but different Z atoms and with the same but with different Z atoms and different / ratio, revealed that the difference between Ni-Mn and Ni-Z nearest neighbor distances decreases as the Z atom changes from In to Sb. This decrease in the local structural distortion accommodates a higher content of Mn until the 2 structure becomes unstable and the alloy undergoes a martensitic transformation.