Low-Temperature Solution Synthesis of Nanocrystalline Binary Intermetallic Compounds Using the Polyol Process

Nanocrystalline intermetallic powders have been synthesized from metal salt precursors at low temperatures using a modified polyol process with tetraethylene glycol as the solvent. This solution route has yielded several phase-pure compounds in the M−Sn (M = Ag, Au, Co, Cu, Fe, Ni), Pt−M' (M' = Bi, Pb, Sb, Sn), and Co−Sb bimetallic systems. In the Co−Sb system, CoSb and CoSb3 can be selectively produced by controlling the initial metal concentrations and the reaction temperature. The Co−Sn and Cu−Sn systems can selectively form Co3Sn2 vs CoSn and Cu6Sn5 vs Cu41Sn11 during a single reaction as a function of temperature. These results demonstrate kinetic control over crystal structure in these intermetallic systems. The reaction progress may be monitored at different times and temperatures by XRD, giving insight into the reaction pathways. TEM micrographs show that the particle sizes in the M−Sn systems range from 5 to 50 nm, while the Pt−M' systems range from 10 to 100 nm. SEM micrographs show that these particles aggregate to form densely packed 100−200 nm clusters. DSC data show that the intermetallics synthesized using the polyol process exhibit order−disorder phase transitions at temperatures near those expected for bulk powders. The nanocrystalline powders are re-dispersible in solution, and preliminary experiments have shown that they may be templated by nanoscale molds, allowing for solution-based materials processing applications.