MÖssbauer Study of a Tinife Shape Memory Alloy.

Mossbauer spectroscopy is very sensitive to structural transitions that may occur during a phase change of the type known to arise in the shape memory TiNiFe alloy. In this work we present the results of resistance vs temperature, differential scanning calorimetry (DSC) and Mossbauer spectroscopy (MS) measurements in Ti50Ni47Fe3 sample. The resistance vs temperature curve shows the usual sharp increase associated to the B2 → R transition at Tp = 245 K and then raises until a maximum is attained at ~ 150 K. The DSC curve shows a peak maximum at the same temperature where the resistivity starts to increase. The room temperature Mossbauer spectrum consists of a single line, indicating that the iron atoms have cubic surroundings. As temperature is lowered, a small asymmetric quadrupole doublet begins to develop. The isomer shift (I.S.) and quadrupole splitting (ΔQ) values of this doublet increase with decreasing temperature until almost constant values are achieved at temperatures ~ 100 K. We relate the changes in the Mossbauer spectra with previously proposed charge density wave induced premartensitic transition.