Ordered Intermetallic Pt–Sn Nanoparticles: Exploring Ordering Behavior across the Bulk Phase Diagram

Abstract

Because the bulk phase diagram of Pt–Sn contains five different compounds (Pt3Sn, PtSn, Pt2Sn3, PtSn2, and PtSn4) with very different congruent or incongruent melting points, we chose this system to investigate factors that influence the homogeneity and structure of intermetallic nanoparticles with different compositions prepared by the same solution phase co-reduction reaction. Pt and Sn chloride precursors were reduced by alkali metal borohydrides in tetrahydrofuran. Of the five compositions, only PtSn forms ordered intermetallic nanoparticles (average domain size of 4.3 nm) at room temperature. As-prepared Pt3Sn nanoparticles adopt an alloy FCC structure and ordered into the cubic Cu3Au structure at the unexpectedly low annealing temperature of 200 °C. Despite their low bulk incongruent melting temperatures, the tin-rich compositions (PtSnx, where x = 3/2, 2, or 4), by contrast, form highly disordered products at room temperature and require annealing at ≥200 °C for crystallization and ordering to be o...