On the contribution of triple junctions to the structure and properties of nanocrystalline materials

Nanocrystalline materials, having a crystal size less than ~10 rim, have been shown to possess unusual properties [1-3]. These properties are primarily the result of a substantial fraction of the atoms (20 50%) lying in intercrystalline regions [3]. On the basis of x-ray scattering [4], EXAFS [5], hydrogen solubility [6], small angle neutron scattering [7], and self diffusivity measurements [8] conducted on bulk nanocrystalline materials, it has been suggested [3] that the grain boundaries in these materials are more disordered than those in conventional polycrystals. Recent studies[9,10] involving direct observation of nanocrystalline interfaces by HREM, provide contradictory results. Wunderlich and co-workers[9] have shown that interfaces in nanocrystalline Pd show an 'extended' structure not typically observed in conventional systems. However, Thomas et al [10] observed that the interfacial structure of nanocrystalline Pd is consistent with that typically observed in coarse-grained materials.