STRUCTURAL TRANSITIONS IN A TINIFE SHAPE-MEMORY ALLOY

Results for resistance versus temperature, differential scanning calorimetry (DSC), Mossbauer spectroscopy, and magnetic susceptibility measurements in a Ti50Ni47Fe3 sample are presented. The resistance versus temperature curve shows a sharp increase at 245K and then rises slowly until a maximum is attained at almost-equal-to 150K. The DSC curve also exhibits a peak at the former temperature. The room temperature Mossbauer spectrum consists of a single line. As the temperature is lowered to 270K, a small asymmetric quadrupole doublet appears. The isomer shift and quadrupole splitting values of this doublet increase with decreasing temperature until almost constant values are achieved at temperatures almost-equal-to 100K. The magnetic susceptibility curve shows a sharp decrease that begins at 255K and then an unexpected increase at 90K. We relate these observations with a charge density wave-driven premartensitic transition in this system, and with the final martensitic phase.