NEGATIVE TEMPERATURE-COEFFICIENT OF ELECTRICAL-RESISTIVITY IN B2-TYPETI-NI ALLOYS

A negative temperature coefficient of electrical resistivity (TCR) has been observed in Ti50-XNi50+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 (rho(20) K/rho(350) K) decreases with increasing Ni content. X-r ay diffraction ana magnetic susceptibility measurements show that a ne gative TCR is not caused by structural phase transition nor by magneti c transition. The Debye temperature of Ti48Ni52, Obtained from the ana lysis of specific heat measurements, is quite low (217 K) and its spin relaxation process has a time duration between 400 mu s and 20 ms, su ggesting that some lattice instability exists. Based on these results, the origin of a negative TCR is discussed.