The phase transition in palladium-manganese alloys with up to 33.3 at.% Mn

Abstract

Abstract Phase transitions in Pd-Mn alloys with 10.0–33.3 at.% Mn were studied by metallographic observations, X-ray and electron diffraction, and electrical resistance measurements. The annealed alloys with 12.5–21.5 at.% Mn obtained by slow cooling from 1153 K were found to exhibit a diffuse scattering in their electron diffraction patterns due to shortrange order of the α-Ll2-s (Ag3Mg type) superstructure with a domain size M=2, and the annealed alloys with 23.0–31.0 at.% Mn had a relatively high degree of α-Ll2-s(M=2) order. Furthermore, for the 29.0–31.0 at.% Mn alloys, in addition to the α-Ll2-s structure, another two structures were observed: one a β1-Ll2-s superstructure, which also has a one-dimensional long-period antiphase domain with M=2 derived from CuAu(I) (Llo type), i.e. a β1 phase with an f.c.t. structure and a c/a ratio of less than unity, and the other an Ll2-type structure of the β2 phase, which is also an f.c.t. structure but has a c/a ratio greater than unity. The β1-Ll2-s(M=2), and β2 phases were also observed for an annealed 33.3 at.% Mn alloy. The phase transitions are discussed in the light of the previously reported phase diagram.