Ordered Structures and Partial Phase Diagram of Pd-rich Palladium-Manganese Alloys Studied by Electron Diffraction and Microscopy

Abstract

In order to present the phase relation in Pd-rich Pd-Mn alloys, we investigated the ordered structures on the basis of transmission electron diffraction and microscopy studies. Among various ordered phases reported up to now, four of Pd₃Mn (D0₂₃), Pd₂Mn, Pd₅Mn₃ and PdMn (L1₀) phases were confirmed to be stable, but no indications of Pd₃Mn I (L1₂) and Pd₂₁Mn₁₁ phases were obtained. In the region of 1d-APS from Pd₃ Mn to about 35 at% Mn, c₀/a₀ gradually decreased from unity with increasing Mn content, indicating the deviation of structure from D0₂₃. The value of M of the 1d-APS was 2.00 up to about 30 at% Mn irrespective of annealing temperature, and then gradually increased to 2.87 with increasing Mn and elevating temperature. Controversial results on M reported by different investigators are ascribed to the annealing temperature as well as composition dependence of M. The structural models reported for Pd₂Mn and Pd₅Mn₃ phases were supported by the present study. We finally propose a partial atomic phase diagram in Pd-rich region.