A stable non-face-centered-cubic phase in noble metal nanoparticles has been reported for this first time by researchers at the Center for Nanoscale Materials (Nanophotonics & NanoBio Interfaces Groups) working with colleagues at the Advanced Photon Source and Electron Microscopy Center. By taking advantage of the availability of this collective array of the DOE Office of Science’s scientific user facilities at Argonne, a stable body-centered tetragonal phase was revealed to exist in silver nanowires with fivefold twinning, even at ambient conditions.
Crystallization of noble metal atoms typically leads to the highly symmetric face-centered-cubic phase that represents the thermo-dynamically stable structure. Introducing defective microstructures into a metal crystal lattice may induce distortions to form non-face-centered-cubic phases when the lateral dimensions of objects decrease to the nanometer scale.
The body-centered tetragonal phase originates from the distortion of cubic silver lattices due to internal strains in the twinned nanowires. The lattice distortion in the center of such a nanowire is larger than that in the surfaces, indicating that the nanowire is composed of a highly strained core encapsulated in a less strained sheath that helps stabilize the strained core. This effect is expected to significantly affect the mechanical properties of the nanowires.
Y. Sun et al., “Ambient-stable tetragonal phase in silver nanostructures,” Nature Communications, 3, 971 (2012). DOI: DOI: 10.1038/ncomms1963 (online)