X-ray Diffraction Study of the Ordered Structures and Phase Relation in Pd-Mn Alloy System

Abstract

This paper reports the results of structural study on the ordered phases formed in Pd-rich Pd-Mn alloys adopting X-ray powder diffraction method. Formations of the tetragonal D0₂₃-type Pd₃Mn, orthorhombic Pd₂Mn and orthorhombic Pd₅Mn₃ reported by previous researchers have been confirmed. Rietveld refinement of the diffraction data of the latter two phases has determined precisely the atomic parameters and revealed the significance of the shifts of atoms in Pd₂Mn. It is shown that the L1₀-type phase extends to about 33 at% Mn at high temperatures and Pd₂Mn and Pd₅Mn₃ form via two-step ordering from the L1₀-type phase. A revised phase diagram on the Pd-rich side has been proposed. Discussion is given on the stability of the relevant ordered phases by making calculation of the total energy by the density functional method.