Faceting of the 3 coincidence tilt boundary in Nb

Due to their unusual properties, the grain boundaries (GBs) with the lowest possible inverse density of coincidence sites =3 play a special role in the GB engineering. The as-grown shape of the cylindric tilt grain boundary (GB) in Nb bicrystal grown by the floating zone method has been studied with the electron back-scattering diffraction method. Both grains form the superlattice called coincidence site lattice (CSL) with the lowest possible inverse density of coincidence sites =3. Four different CSL facets (100) 3CSL, {110} 3CSL, {120} 3CSL and {210} 3CSL were observed simultaneously. Flat facets (100) 3CSL , {110} 3CSL, {120} 3CSL and {210} 3CSL form smooth edges (no slope discontinuity) with rounded rough GB portions. Rough surface curves away from the plane of the (–1, 2, 0) 3CSL facet at the edge with (–1, 1, 0) 3CSL facet as xβ with β = 1.61 ± 0.09. At the edge between (210) 3CSL and (–1, 2, 0) 3CSL facets β = 1.46 ± 0.09. Both values reveal the GB roughening belonging to the Pokrovsky-Talapov universality class. It has been shown for Pb surfaces [K. Arenhold, S. Surnev, P. Coenen, H.P. Bonzel and P. Wynblatt, Surf. Sci. 417 (1998) L1160] that the β value depend on the details of the steps interaction at the vicinal surface. In our case the difference between measured β for two different facet edges can be due to the similar details of GB steps. C 2005 Springer Science + Business Media, Inc.