Thermopower behavior for the shape memory alloy NiTi

We report thermopower measurements for the nickel titanium shape memory alloy Ni0.507Ti0.493. Our measurements reveal abrupt changes in the temperature dependence of thermopower, which correlate well with the structural phase transition between the austenitic and martensitic phases. These transition effects in thermopower are more clearly defined than in the resistivity, which is also reported. In the martensitic phase, thermopower exhibits standard metallic diffusion behavior with a nonlinearity, which is consistent with either a small peak in the density of states just below the Fermi level, as calculated by Kulkova, Egorushkin, and Kalchikhin [Solid State Commun. 77, 667 (1991)], or else electron-phonon mass enhancement. For thermally or mechanically treated samples, the magnitude of the transition effects in thermopower are reduced. (C) 2001 American Institute of Physics.