25th anniversary article: exploring nanoscaled matter from speciation to phase diagrams: metal phosphide nanoparticles as a case of study.

The notions of nanoscale "phase speciation" and "phase diagram" are defined and discussed in terms of kinetic and thermodynamic controls, based on the case of metal phosphide nanoparticles. After an overview of the most successful synthetic routes for these exotic nanomaterials, the cases of InP, Ni2 P, Ni12 P5 and Pdx Py are discussed in detail to highlight the relationship between composition, structure, and size at the nanoscale. The influence of morphology is discussed next by comparing the behavior of Cu3 P nanophases with those of Nix Py , FeP/Fe2 P, and CoP/Co2 P. Perspectives provide the reader with methodological guidelines for further investigation of nanoscale "phase diagrams", and their use for optimized synthesis of new functional nanomaterials.