Calculations were made of the contribution, to the total enthalpy of nanocrystalline computer-generated samples, which arose from grain boundaries and triple junctions. It was shown that the excess enthalpy per unit volume (excess enthalpy density) at the triple junctions was essentially the same as that found for grain boundaries. This implied that triple junctions and grain boundaries constituted equivalent departures from a perfect crystal structure; at least in the present context. By taking proper account of the numbers of grain boundaries and triple junctions, it was shown that reported observations of decreasing grain-boundary energy, with decreasing grain size in nanocrystallized amorphous Se, and of a negative triple-junction line tension in computer simulation results, were the consequences of neglecting the relationship between grain-boundary width and grain size. These could be of the same order of magnitude in the nanophase regime.

Grain Boundary and Triple Junction Enthalpies in Nanocrystalline Metals. A.Caro, H.Van Swygenhoven: Physical Review B, 2001, 63[13], 134101 (5pp)