Effect of magnetism on surface segregation in FeNi alloys.

Modelling the segregation of the various chemical species in the vicinity of crystallographic defects in FeNi alloys is essential because it affects the macroscopic properties of these materials, which are widely used in technological applications. We present here a theoretical study of surface segregation, within a mean-field approach based on the tight-binding Ising model grounded on density functional theory calculations. The most important result is that, although FeNi presents none of the driving forces (i.

Atomistic modelling of residual stress at UO2 surfaces.

Modelling oxide surface behaviour is of both technological and fundamental interest. In particular, in the case of the UO2 system, which is of major importance in the nuclear industry, it is essential to account for the link between microstructure and macroscopic mechanical properties. Indeed micromechanical models at the mesoscale need to be supplied by the energetic and stress data calculated at the nanoscale.

How to derive tight-binding spd potentials? Application to zirconium.

We propose here a general methodology to derive tight-binding potentials accounting for spd hybridization in transition metals, dealing simultaneously with electronic structure and energy properties. This methodology is illustrated for zirconium which is largely used for technological applications, in particular in the nuclear industry, and whose modelling is known to be complex and challenging. Such potentials are very promising.

Theoretical study of xenon adsorption in UO2 nanoporous matrices.

We present a theoretical study of xenon incorporation in UO2 nanocavities, by means of Grand Canonical Monte Carlo calculations based on semi-empirical potentials. We first characterize the reconstruction of the matrix around an empty cavity which leads to a stoechiometry change from UO2 to UO in this region. Then, we determine xenon adsorption isotherms which exhibit an abrupt transition from a dilute phase to a dense one and an increase in the density of the latter phase as a function of temperature.

Cu-Ag (111) polymorphism induced by segregation and advacancies.

Chemical and structural phase transitions induced by Ag surface segregation in the dilute Cu(Ag) (111) system have been investigated by Monte Carlo simulations. The polymorphism observed when depositing Ag on Cu (111) is proven to exist also in equilibrium segregation. If the segregation isotherms are not very sensitive to the superstructures, we show that the superstructure observed in the high part of the isotherm depends strongly on the number of advacancies.