Metallurgy in a beaker: Nanoparticle toolkit for the rapid low-temperature solution synthesis of functional multimetallic solid-state materials

Intermetallic compounds and alloys are traditionally synthesized by heating mixtures of metal powders to high temperatures for long periods of time. A low-temperature solution-based alternative has been developed, and this strategy exploits the enhanced reactivity of nanoparticles and the nanometer diffusion distances afforded by binary nanocomposite precursors. Prereduced metal nanoparticles are combined in known ratios, and they form nanomodulated composites that rapidly transform into intermetallics and alloys upon heating at low temperatures. The approach is general in terms of accessible compositions, structures, and morphologies. Multiple compounds in the same binary system can be readily accessed; e.g., AuCu, AuCu₃, Au₃Cu, and the AuCu-II superlattice are all accessible in the Au-Cu system. This concept can be extended to other binary systems, including the intermetallics FePt ₃, CoPt, CuPt, and Cu₃-Pt and the alloys Ag-Pt, Au-Pd, and Ni-Pt. The ternary intermetallic Ag₂Pd₃S can also be rapidly synthesized at low temperatures from a nanocomposite precursor comprised of Ag₂S and Pd nanoparticles. Using this low-temperature solution-based approach, a variety of morphologically diverse nanomaterials are accessible: surface-confined thin films (planar and nonplanar supports), free-standing monoliths, nanomesh materials, inverse opals, and dense gram-scale nanocrystalline powders of intermetallic AuCu. Importantly, the multimetallic materials synthesized using this approach are functional, yielding a room-temperature Fe-Pt ferromagnet, a superconducting sample of Ag ₂Pd₃S (T_c = 1.10 K), and a AuPd₄ alloy that selectively catalyzes the formation of H₂O₂ from H₂ and O₂. Such flexibility in the synthesis and processing of functional intermetallic and alloy materials is unprecedented.