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Regarding the interface between two crystals, the dependence of interfacial properties on crystallographic parameters is more complex than for surfaces, because the interfacial phenomena vary with not only the orientation of the interface but also the orientation relationship between the two crystals.

Much less is known about the behavior of interfaces than that of surfaces because experimental techniques for the study of interfaces are much more limited than for surfaces. At interfaces, atomic relaxation can take a number of different forms, including elemental segregation, formation of particles, emission of partial dislocations [1] and formation of extended structures, or dissociation [2–4].

In most cases, the interface between two crystals is not ideal. It is very common that the atomic number of the interface is lower than those of the crystalline bulks and there is chemical intermixing between them. For instance, nickel oxide (NiO) nanocrystals epitaxially grown on (001) strontium titanate (SrTiO₃) single crystal substrates had been characterized by aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and the rough and irregular interface between the NiO and SrTiO₃ crystals had a lower average atomic number than the two crystalline bulks. [5] (see page1352)

[1] J. D. Rittner, D.N. Seidman, and K. L. Merkle, Phys. Rev. B 53, R4241 (1996).
[2] K. L. Merkle, Microsc. Microanal. 3, 339 (1997).
[3] J. D. Rittner and D. N. Seidman, Phys. Rev. B 54, 6999 (1996).
[4] K. L. Merkle, J. Phys. Chem. Solids 55, 991 (1994).
[5] Xuan Cheng, Jivika Sullaphen, Matthew Weyland, Hongwei Liu, and Nagarajan Valanoor, Role of interface structure and chemistry in resistive switching of NiO nanocrystals on SrTiO3, APL Materials 2, 032109 (2014).