Cu₃Sn – understanding the systematic absences

Abstract

The intermetallic compound Cu3Sn has previously been described as a long-period antiphase boundary superstructure of the Cu3Ti structure type. While the compound itself has been reported as a tenfold and an eightfold superstructure, ternary doped alloys show shorter repetitions. Interestingly, the diffraction patterns of these compounds show non-crystallographic absences that cannot be explained using the superstructure models. Since the compound exhibits phase broadening, these models are not satisfactory because the paucity of observed data does not allow for a refinement of the composition. Here, an alternative, superspace model in the orthorhombic space group Xmcm(0β0)000 is proposed, with the centering vectors (0,0,0,0) and (½,0,0,½). The presence of the non-crystallographic absences is explained as a result of a dominating occupational modulation that is accompanied by a weaker displacive modulation. In consistency with the EDXS results, the composition has been refined to Cu3 + xSn from single-crystal X-ray diffraction data. It is further demonstrated that by varying the length and the direction of the modulation wavevector in the superspace model, the ternary Cu3Sn compounds and other colored hexagonal close packing (h.c.p.) structures can be produced.

Stable and Metastable Phase Equilibria Involving the Cu6Sn5 Intermetallic

“…The ε-Cu 3 Sn phase is labelled by Cu 3 Sn. Although there are different reported superstructures[16][17][18][19][20] , we have no indication for phase transitions of that phase from our work, and the crystal structure models from Refs. 19, 20 appear to describe the ordering of Cu vs. Sn most appropriately.…”

“…was preferred. The latter choice basically corresponds to a disordered version of the superstructures reported in the literature [16][17][18][19][20] and avoids the problems associated with distinction between pseudo-symmetric orientations, which is most likely not possible with the available Kikuchi patterns (see also footnote 1). The η phase was described hexagonal with a = 4.22 Å and c = 5.11 Å (P6 3 /mmc symmetry), whereas the η′′ was tentatively described in terms of the average structure with a = 4.22 Å, b = 7.32 Å, c = 5.11 Å and β = 90.23° (C2/c symmetry), not taking into account the atomic ordering (cf.…”

Crystal structure of incommensurate ηʺ-Cu1.235Sn intermetallic

“…The refinement model further included a second, hexagonal phase used to describe the relevant reflections due to the Cu 3 Sn phase and having a crystal structure according to Ref. [22,23]. That phase was present due to the overall alloy composition corresponding to 43 at.% Sn and this phase was also visible in optical micrographs of the microstructure, see supplementary material of Ref.…”

Stabilization of the ζ-Cu10Sn3 Phase by Ni at Soldering-Relevant Temperatures

“…a e-Cu 3 Sn contains periodic antiphase boundaries, which are not considered by the Knödler model 29. Watanabe et al30 and Mueller and Lidin31 consider this issue by creating superstructures containing such antiphase boundaries b In contrast to early descriptions of the atomic structure as simple NiAs type,32 this disordered high-temperature g phase can be described as Cu(1)Cu(2) 0.2 Sn instead of Cu 6 Sn 5 . The Sn atoms form a hexagonally closed packed arrangement with Cu(1) occupying the octahedral sites, whereas the Cu(2) atoms occupy one-fifth of the trigonal bipyramidal sites formed by Sn34 …”