Determination of the equilibrium miscibility gap in the Pd–Rh alloy system using metal nanopowders obtained by decomposition of coordination compounds

•The Pd–Rh phase diagram has been experimentally reinvestigated.•The true equilibrium was achieved with the two-way approach.•The critical point of the miscibility gap lie at 58at.% Rh and 820°C. The Pd–Rh phase diagram has been reinvestigated in the subsolidus region using X-ray diffraction, scanning and transmission electron microscopy. The true equilibrium at the miscibility boundary was achieved with the two-way approach. Nanosized powders of metastable solid solutions and two-phase palladium–rhodium mixtures were used to shorten the time required to equilibrate the system. The initial samples were prepared by decomposition of coordination compounds [Pd(NH3)2Cl2], [Rh(NH3)5Cl]Cl2, [Pd(NH3)4]3[Rh(NO2)6]2 and [Pd(NH3)4][Rh(NH3)(NO2)5]. The obtained phase diagram exhibits miscibility gap wider than generally accepted with the critical point of solubility at 58at.% Rh and 820°C.