Phase transformation behavior in nanoalloys

Nanomaterials are now well established as a distinct class of materials. Among them, the nanoparticles of metals and alloys constitute an important subclass that has attracted wide attention from the point of view of scientific understanding and wide domain of potential applications. The present review primarily deals with alloy nanoparticles or nanoalloys containing more than one element having single or multiphase microstructure. Both free, as well as embedded alloy nanoparticles, will be considered. The physical and chemical properties of nanoalloys can be tuned by manipulating the type of metals, their compositions, and the degree of the atomic arrangement, shape, and size. These are often controlled by phase transformation. The present article reviews the recent advances in phase transformation behaviour of the alloy nanoparticles by focussing on the single and biphasic alloy of free and embedded nanoparticles; the effect of size, shape, and chemical order on the phase transformation and alloying at the nanoscale. Particular emphasis will be on melting, solidification, and order-to-disorder transformation, taking into account the extensive and detailed theoretical analysis available using thermodynamics and kinetics. Wherever needed, we shall compare free and embedded nanoparticles and invoke the results of elemental metal nanoparticles to highlight the similarities and differences. Towards the end, the unresolved issues and future directions of research on nanoalloys will be deliberated.