The surface-area-difference (SAD) model is developed for the cohesive energy of metallic crystals by taking into account surface effects, and has been extended to predict the thermodynamic properties of metallic nanoparticles, nanowires and nanofilms with free and non-free surfaces (embedded in a matrix). It is found that the thermodynamic properties of metallic nanocrystals depend on the crystal size and the interface coherence, where the interface coherence determines the variation tendency (increasing or decreasing), and the size determines the magnitude of the variation. The present calculated results on the thermodynamic properties of metallic nanocrystals by the SAD model are consistent with the corresponding experimental values.

PACS 65.80.+n, 82.60.QrThe thermal stability of metal nanoparticles is discussed in both melting thermodynamics and interface thermodynamics. Emphases are put on the size and shape dependence of melting temperature, critical size and vacancy-formation energy of both freestanding and embedded metal nanoparticles. The melting temperature depression and superheating phenomena for reported nanoparticle systems are explained. Critical sizes of Fe, Co, Ni metal nanocrystals that the crystals keep their crystallinity are calculated and the corresponding minimum melting temperatures predicted. The vacancy-formation energies of Fe, Co, Ni small particles are also calculated as a reference. Theoretical predictions are consistent with experimental results.

Considering the different effects of exterior atoms (face, edge and corner atoms), the Bragg–Williams model is generalized to account for the size, shape and composition-dependent order–disorder transition of bimetallic nanoparticles (NPs) with B2, L10 and L12 ordered structures. The results show that the order–disorder temperatures T C,p are different for different shapes even in the identical particle size. The order of order–disorder temperatures of different shapes varies for different sizes. The long-range order parameter decreases with the increase in temperature in all size ranges and decreases smoothly in large sizes, but drops dramatically in small sizes. Moreover, it is also found that the order–disorder temperature of bimetallic NPs rises with increasing particle sizes and decreases with a deviation from the ideal compositions. The present predictions are consistent with the available literature results, indicating its capability in predicting other order–disorder transition phenomena of bimetallic NPs.

A simplified model that describes the size and shape dependence of melting thermodynamics of full free nanocrystals was established. Critical sizes of Fe, Co, Ni magnetic nanocrystals when the crystals keep their crystallinity were calculated and the corresponding minimum melting temperature was predicted. Theoretical predictions were consistent with experimental results.