Defect structures in solution-grown single crystals of the intermetallic compound Ag3Sn

The compound Ag3Sn adopts the ordered orthorhombic D0(a) Cu3Ti-type structure. It exhibits an unusual low yield stress and high ductility for an intermetallic compound, but the reasons for these effects are not clear. Here, we report an electron microscopy study on the defects present in solution-grown Ag3Sn single crystals that have deformed during the decanting and subsequent handling processes. It is found that the crystals contain two types of lenticular deformation twins: {011}-type and {211}-type. These twins interpenetrate with no evidence of cracking at the intersections. The crystals also contain high densities of dislocations including long straight dipoles with b = +/- [010] and shorter curved segments and loops with b = [10 (2) over bar] and [001]. It is inferred that the dipoles are artifacts of specimen preparation that climb in from the cross-sectional sample surfaces, whereas the shorter segments are deformation debris. If a combination of twinning and dislocation glide of the types observed here were to form concurrently during general deformation of Ag3Sn, then they could provide the necessary number of independent deformation modes to accommodate an arbitrary plastic strain, which might help to explain the unusual ductility of this compound.