Among the abundant literature on nanoparticles, metal borides and phosphides account for just 2% of published articles. However, these materials were synthesized in bulk form as early as the 18th and 19th centuries by German and French teams. Indeed, the first phosphides were discovered by Andreas Margraff and Bertrand Pelletier, while almost a century later Léopold Gemlin, C. Decotil and Richard Lassaigne discovered borides. These materials have remarkable properties:
- gallium and Indium phosphides are semiconductors, and are used as frequency-tunable phosphors in light-emitting diodes and optical probes; they are the famous " quantum dots ";
- borides such as MgB2 are superconductors used as magnets in magnetic resonance imaging (MRI).
Systematically synthesizing borides and phosphides of numerous metals on a mesoscopic scale represents a major challenge. All the more so since, at this scale, these "exotic" materials are expected to display highly interesting catalytic and electrochemical properties. This lesson presents recent synthesis efforts and strategies to develop boride and phosphide particles on the mesoscopic scale (5 nm-100 nm). What makes these chemistries difficult is the tendency of these two non-metals to form stable B-B or P-P bond chains (a stronger tendency for boron than for phosphorus) - this is all the more pronounced the higher the non-metal/metal ratio - and their low reactivity towards metals. These peculiarities, combined with the strong covalent character of M-P and M-B bonds, result in relatively high synthesis temperatures that favor the growth of nuclei, making it difficult to maintain metal borides and phosphides on the mesoscopic scale.
