Strain glass in Fe-doped Ti-Ni

We report the existence of strain glass in Ti₅₀Ni _50-xFe_x, beyond a critical Fe doping level x > x _c(5 < x_c < 6). The strain glass state is confirmed by the appearance of a frequency-dependent anomaly in the AC mechanical modulus/loss at a freezing temperature T₀ and by the breaking of ergodicity shown in a zero-field-cooling/field-cooling experiment. Based on the experimental results, a phase diagram is established in which both the normal martensitic transformations (for x < x_c) and the strain glass transition (for x > x_c) are indicated. The new phase diagram allows for explanations of two long-standing puzzles in Ti₅₀Ni _50-xFe_x and Ti-Ni alloys: (i) the origin of nanodomains present prior to the martensitic transformation (for x < x_c) and (ii) the negative temperature dependence of electrical resistivity in abnormal non-transforming compositions (for x > x_c).