Formation and structure of the Al–Mn–Pt “Robinson-type” phase

The stable “Robinson-type” phase (R-phase, Cmcm, a = 7.730 Å, b = 24.035 Å and c = 12.597 Å) was revealed at 700 °C in a small compositional region around Al_79.5Mn₁₆Pt_4.5. Partial phase equilibria in its vicinity were determined at 700 °C. At this temperature, it is in equilibrium with the ternary extension of the Al–Mn T-phase, whose compositional region propagates up to that of the R-phase. An atomic model of the R-phase, containing 124 Al, 24 Mn and 8 Pt atoms, was deduced using direct methods applied to the 3D electron-diffraction tomography data and compared to those of the Al–Mn–Ni R-phase and Al–Mn–Pt(Pd) T-phase.