Electronic structure of Ti–Ni alloys: An XPS and NEXAFS study

The paper reports on a study of the electronic structure of binary homogeneous alloys Ti55Ni45, Ti50Ni50, and Ti45Ni55 by X-ray photoelectron and near-edge X-ray absorption spectroscopies. The experimental data obtained were used to derive the occupied and unoccupied d-states density redistribution upon formation of the Ti–Ni alloys. The Ti and Ni L2,3 X-ray absorption edge intensity measured permitted calculation of the variation of the titanium and nickel d-shell occupancy induced by formation of the Ti50Ni50, Ti55Ni45 and Ti45Ni55 alloys. It is shown that the occupation of the nickel d-band decreases by 0.13 el./atom in formation of the above alloys and practically does not depend on the ratio of the constituent elements, whereas that of the titanium d-shell is strongly dependent on the atomic composition of the alloy. The charge transfer between the components was found to be insignificant; this implies that the change in occupancy of the nickel and titanium d-shells originates from intratomic redistribution of electron density between the d- and sp-states. The Ti50Ni50 equiatomic alloy is unique in that it has the lowest titanium d-shell occupancy and, hence, the largest number of sp-electrons. It is shown that the increasing Ni content in the TiNi alloys leads to a noticeable gain of titanium d-electrons. It is assumed that the additional d-electrons can form a direct bonds, which increases the elastic moduli and, consequently, reduce the temperature of martensitic transformation in Ni-rich TiNi alloys.

► Ti50Ni50, Ti55Ni45 and Ti45Ni55 alloys have been studied with XPS and NEXAFS. ► Nickel and titanium d-states densities redistribute upon Ti–Ni alloys formation. ► Variation of the Ti and Ni d-band occupancy in the Ti–Ni alloys has been estimated. ► Ti atoms get additional d-electrons with increasing of Ni content in Ti–Ni alloys. ► This may be a reason for the reduction of the martensitic transformation temperature.