A negative temperature coefficient of electrical resistivity (TCR) has been observed in Ti50-X Ni50+X (at.%; X=1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5) in the temperature range between 20 and 350 K. The resistivity vs temperature curve has no hysteresis and the relative resistivity at 20 K (ρ20 K/ρ350 K) decreases with increasing Ni content. X-ray diffraction and magnetic susceptibility measurements show that a negative TCR is not caused by structural phase transition nor by magnetic transition. The Debye temperature of Ti48Ni52, obtained from the analysis of specific heat measurements, is quite low (217 K) and its spin relaxation process has a time duration between 400 µs and 20 ms, suggesting that some lattice instability exists. Based on these results, the origin of a negative TCR is discussed.

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