THE TRANSITION OF THE HYDROGEN-INDUCED LI2 ORDERED STRUCTURE OF PD3MN TO THE AG3MG STRUCTURE

In previous papers we have shown that when an initially disordered and an initially ordered alloy (Ag3Mg-type structure) of Pd3Mn were exposed to hydrogen gas at elevated temperatures pH2$GR1 MPa, they transform to an ordered Ll2 structure with an accompanying introduction of large dislocation densities. The goal of this work is to obtain detailed information about the reverse transformation from the hydrogen-induced Ll2 structure to the Ag3Mg structure, using electrical resistance measurements and transmission electron microscopic (TEM) observations. The hydrogen-induced ordere form of Pd3Mn, Ll2, has been shown to be stable in the temperature range 540 to 650 K even in the absence of dissolved hydrogen. The sharp resistance increase noted starting from about 670 K corresponds to the Ll2&rarrAg3Mg transition.