Thermodynamics of surface compositional segregation in Ni–Co nanoparticles

Thermodynamic analysis of a Ni–Co alloy nanoparticle (atomic ratio 1:1) is carried out to study the influence of size effect on surface compositional segregation. The surface compositions of Ni–Co nanoparticles are calculated based on the regular solution model, which takes into account of the size effect, and compared with that of bulk alloy particles with a larger size. It is observed that the segregated surface compositions in the Ni–Co binary alloy single-crystal nanoparticles (with particle diameter of 10–100 nm) are few times larger than that of the corresponding bulk single crystal (with the particle diameter >100 nm). The details of the thermodynamic modeling and the calculated surface compositions due to segregation are discussed.