Internal stress-induced orthorhombic phase in 5-fold-twinned noble metal nanowires

We use atomistic simulations to show that 5-fold-twinned nanowires of several face-centered cubic metals (Ag, Au, Cu, and Pd) exhibit an overall body-centered orthorhombic phase resulting from the large internal stress associated with their twinned structure. The distribution of atomic stress in the nanowires confirms the existence of a disclination at the 5-fold axis, in addition to an anisotropic distortion of the lattice. We find that two regions of the nanowire are highly stressed: local stress maxima are distributed in the shape of leaflets running along each twin boundary, as well as in semicircular regions near the free surfaces. The large elastic strain energy associated with the distortion may be partially released via the formation and propagation of partial dislocations, which are restricted to a single subunit of the nanowire. Our calculations are in line with experiment and indicate the complex ways in which the structures of these metal nanocrystals can depend on their shape.