EELS studies of Ti-bearing materials and ab initio calculations

Electron energy loss spectrometry (EELS) in a transmission electron microscope (TEM) is used to provide information on the local structure, chemical composition and bonding of different titanium compounds. Titanium hydrides (TiHx) and nitrides (TiNx) resulting from insertion of hydrogen and nitrogen ions in titanium alloys have been studied by analysing the low-loss region of the EEL spectrum and by ELNES (energy loss near-edge structure) of the N-K edge by comparison with reference sample spectra and/or ab initio calculations. These investigations have revealed the difficulties and the limits for the quantification of hydrogen in titanium solid solutions. In the case of titanium nitrides, different phases have been identified (δ-TiN, ɛ-Ti2N) as well as vacancies on N-sites in these structures and solid solutions of nitrogen in α-titanium have been quantified. In the same way, a study by ELNES of the C-K edge and the N-K edge has been carried out on whiskers of transition metal carbonitrides (TaxTi1−x)CyNz with the rock-salt structure. The aim of the study was to determine the nitrogen and carbon content as a function of x, and if it is possible to characterise the metal-non-metal bonds in order to propose a model for a substructure in the whiskers.