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, Pd 5Mn3 and PdMn (L10) phases were confirmed to be stable, but no indications of Pd3Mn I (L12) and Pd 21Mn11 phases were obtained. In the region of 1d-APS from Pd3Mn 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 ld-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.