X-ray photoelectron spectroscopy studies of Ti-Al and Ti-Al-V alloys using Cr K? radiation

Electronic structure studies of Ni-X (X: B, S, P) alloys using x-ray photoelectron spectroscopy, x-ray induced Auger electron spectroscopy and density functional theory calculations

The electronic structure of Ni-X (X = B, S, P) alloys was studied using x-ray photoelectron spectroscopy, x-ray induced Auger electron spectroscopy and density functional theory. The spectroscopic data in the form of the Ni 2p shake-up satellite and the Ni 2p LMM, P 2p KLL and S 2p KLL Auger parameters combined with density of states (DOS) and charge difference plots suggest an overall charge transfer from the Ni sites towards the alloying addition sites. However, this is masked, with intra-atomic charge redistribution leading to an increased occupancy of the Ni 3d states in the alloys. The Ni 3d DOS shows strong similarity to that of Pt which is the best catalyst for hydrogen evolution.

Calculations for displacive ω-phase transformations in Ti-Al alloys with Nb additions at finite temperature

We examine by means of first-principles calculations the bcc-like (bcc: body centered cubic) to ω-like phase transformations in Ti-Al alloys with Nb additions at finite temperature. To simulate the alloy we use different discrete atomic configurations in a six atom unit cell of the stoichiometry Ti(3)Al(2)Nb. Calculated ground state energies show an instability in the ternary Ti(3)Al(2)Nb alloy against the ω structure type atomic displacement. To better understand the role of entropy in the stability/instability of these systems, the first-principles calculations are extended to finite temperature by including various contributions to the free energy. In particular, the vibrational free energy is calculated within a quasiharmonic approximation. It is shown that the bcc structure is stabilized by the contribution of the low energy modes to the lattice entropy against ω type atomic displacements. We find that configurational entropy plays a major role in the ω to B8(2) transformation. Calculated lattice parameters and transition temperatures are found to be in excellent agreement with experiment.