EPJ Special Topics

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Eur. Phys. J. Special Topics 158, 1-5 (2008)
DOI: 10.1140/epjst/e2008-00645-7

Origin of diffuse scattering appearing in iron-doped Ti-Ni shape memory alloys

T. Yamamoto, M.-S. Choi, S. Majima, T. Fukuda and T. Kakeshita

Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan

fukuda@mat.eng.osaka-u.ac.jp

(Published online: 1 May 2008)

Abstract
We have investigated diffuse scattering appearing in Ti-Ni based shape memory alloys to understand the origin of instability of the B2-type structure in the system. Transmission electron microscope observation and a first-principle electronic structure calculation have been made for Ti-(50-x)Ni-x Fe (x = 6, 7, 8, 10). They exhibit diffuse scattering in the electron diffraction pattern along $\langle\xi\xi 0 \rangle^{*}$ direction on cooling with the intensity peak located at incommensurate positions of $q_{\rm {diffuse}} = \langle \zeta\zeta 0 \rangle^{*}$ . The value $\zeta$ increases with decreasing temperature for all alloys. The temperature at which the incommensurate scattering start to appear is close to the one at which the electrical resistivity exhibits a local minimum, $T_{\rm {min}}$ , for all the alloys. The value of $q_{\rm {diffuse}}$ at $T_{\rm {min}}$ is nearly the same as the nesting vector of Fermi surface at $T_{\rm {min}}$ , which is obtained by calculating the generalized susceptibility of the B2-type structure along the $\langle\xi\xi 0 \rangle^{*}$ direction. These results strongly suggest that the nesting effect of Fermi surface is responsible for the instability of the B2-type structure in Ti-Ni based shape memory alloys.