Crystals are distinguished from other states of matter by the existence of long range order or periodicity. Glasses or amorphous materials lack long range order. Nevertheless, it is possible that bond distances and coordination numbers exhibit narrow distributions. The disorder in glasses is homogeneously distributed whereas in nanocrystalline solids a heterogenously distributed disorder is generated by interrupting the periodicity of crystals by interfaces. A simple model of nanocrystalline materials distinguishes between crystalline grains and a network of interfaces, i.e. grain boundaries and pore surfaces.

Scattering techniques provide structural information on ordered as well as disordered materials. Diffraction by the crystal lattice emphasizes the long range order which may obscure the diffuse scattering from disorder whereas spectroscopy by a local probe is dominated by short range order. Spectroscopic techniques and EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy in particular provide complementary information on the structure of nanocrystalline materials where order and disorder coexist.

Diffraction methods such as X-ray, electron or neutron diffraction rely on the long range order of materials to extract structural information. This is easily seen by the Scherrer broadening of the diffraction peaks when the crystal size decreases, i.e., the accuracy of the structural information decreases with decreasing grain size. Scattering experiments using the same probes can also provide structural information in case of highly disordered materials.

Spectroscopic methods such as NMR (Nuclear Magnetic Resonance) or EXAFS provide structural information down to the molecular level. However, in case of large disorder the data analysis is very demanding. It is possible to investigate the local structure of nanomaterials by XAFS .

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