Theoretical investigation of the hydrogenation induced atomic rearrangements in palladium rich intermetallic compounds MPd3 (M = Mg, In, Tl)

Based on results from density-functional calculations we present an interesting and unusual mechanism for a structural change in a certain class of intermetallic compounds that can be induced through hydrogen absorption. Through an atomic rearrangement, palladium-rich intermetallic compounds MPd3 (M = Mg, In, Tl) can change the structure from a tetragonal ZrAl3 or TiAl3 type to a cubic AuCu3 type structure. Within the density-functional calculations we study a possible reaction pathway via a gliding of atomic layers with and without the presence of hydrogen. Subsequently, we argue that H-Pd interactions can be held responsible for the structural change upon hydrogen uptake, and that entropic and packing effects can explain the existence of the lower-symmetric structures in the absence of hydrogen.