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Cyrstal Structure Stability

  1. Feb 28, 2007 #1
    Hello,

    I was curious as to what you think of the paper below. This concerns the effects of substitution in a NiTi lattice on the transformation temperatures. The author seems to draw from this study, that since Nickel has comparatively localized electrons, the increase in temperature stabilizes Ni bonds with neighboring atoms. Since the Ni and Ti atoms are packed in a ordered fashion in the B2 structure, the weakening of Ni bonds with a decrease in temperature, results essentially in the shearing of a plane of atoms, changing the crystal structure from B2 (CsCl) to Bl9' (distorted face centered). Essentially the bonds between Ti atoms in the lattice remain strong, and with the coresponding weakening of the Ni bonds, the Ti atoms come closer together and the Ni are pushed apart. Consequently subsitituting atoms with varying electronegativities alters the transformation temperatures, expected from this theory.
    Is this explaination for the transformation in memory alloys such as nitinol, mainstream? I mean is this a widely excepted theory, or is it disputable to your knowledge? Also if you notice any misconceptions I have, would you please point them out. Any additional papers you may know concerning the topic would be welcomed too.

    http://www.public.iastate.edu/~svetinol/papers/articleicomat.pdf

    Thanks,
    -scott
     
  2. jcsd
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