Competition or synergy between surface segregation and bulk ordering: the CuPd system
The theoretical segregation isotherm in CucPd1-c(111) has been studied both in the disordered and in the ordered state within an energetic model derived from the electronic structure. A segregation reversal is obtained as a function of the bulk concentration in the disordered state. In the ordered state, we obtain a great variety of surface critical behaviours: whereas the bulk order-disorder or order-order transitions are of first order, the surface ones can be of first or second order. In this last case, a wetting behaviour is shown.