Formation of the L12 ordered structure in hypostoichiometric Pd3Mn alloys containing interstitial boron

The ordering of the L12 structure in hypostoichiometric Pd3Mn alloys containing interstitial boron, i.e. Pd3+xMn1-xBy with x = 0.2 and 0.4 and y = 0.27 and 0.53, and for comparison in Pd3.2Mn0.8M0.27 with substitutional alloying elements M≡Ag, Cu and Ni has been studied by X-ray, electron diffraction and electrical resistance measurements. The results clearly indicate the presence of the L12 (Cu3Au) type of superlattice in addition to small amounts of regions containing superimposed L12-s and L12 superlattices. For alloys of Pd3.4Mn0.6By with y = 0.27 and Pd3.2Mn0.8M0.27 with M≡Ag, Cu and Ni, however, this was not the case. It is suggested that the formation of the L12 structure in the alloys at high temperature requires the presence of the L12-s structure and an interstitial boron content greater than about y = 0.15. Thus the order transition L12-s&rarrL12 in Pd3+xMn1-xBy is associated with the preferential occupation of boron atoms at particular octahedral sites of the L12-s structure.