The electronic structure study of titanium-nickel alloys by x-ray photoelectron spectroscopy

Purpose of the study. The purpose of the study was to investigate the electronic structure changes of titanium-nickel (Ti-Ni) alloys. The electronic structure was correlated with the physical property of shape memory effect demonstrated by 50% atomic nickel concentration Ti-Ni crystalline alloys.;Methodology. The technique of x-ray photoelectron spectroscopy was used to collect spectra using an ESCA PHI 5100 system. The spectra were analyzed by measuring binding energies, Auger parameters, Shirley and Tougaard backgrounds, and electronegativity criteria. Changes in the density of state (DOS) at the Fermi level were modeled using binding energy shifts, Auger parameter changes, the intrinsic loss structure modeled from the Shirley and Tougaard background, and the electronegativity criteria.;Results. Significant changes in binding energy (BE) were noted for alloys, but changes in BE could not be with electronegativity criteria. The Auger parameter demonstrated positive values for Ti and negative values for Ni with minimum values at the 50% atomic nickel concentration. This was interpreted as a transfer of charge from nickel to titanium. Wagner plots of the Auger parameter indicated Ti and Ni were in different chemical states in each of the alloys with a minimum for the 50% atomic concentration nickel, which correlates to the shape memory effect (SME). Chemical shifts indicated a shift in charge from Ni to Ti, correlating to the results yielded by the Auger parameter. Normalized background analysis (indicative of the intrinsic loss structure) obtained from Shirley and Tougaard methods correlated well with the Auger parameter and chemical shift results, indicating that background analysis is useful for studying changes in chemical state for these materials.;Conclusions. This study demonstrated that BE shifts and electronegativity criteria can not be successfully used to model changes in chemical states for Ti-Ni alloys. The results from Auger parameter analysis, chemical shift analysis, and intrinsic loss structure as given by background analysis correlate well with each other and indicate a transfer of charge from Ni to Ti with significant differences in chemical state for the 50% atomic nickel concentration, which corresponds well with the SME.