The microstructure is defined by the type, crystal structure, number, shape and topological arrangement of phases and defects such as point defects, dislocations, stacking faults or grain boundaries in a crystalline material. Nanocrystalline materials are polycrystalline solids with grain sizes below 100 nm. Grains as well as pores, interfaces and other defects are of similar dimensions. This nano-specific microstructure (nanostructure) leads to chemical and physical size effects.
It is a prerequisite for the understanding of properties of nanomaterials to have a detailed knowledge of the structure from the atomic/molecular (local) to the crystal structure (long range order) and to the microstructure (mesoscopic scale and defect structure). Consequently, various analytical techniques are required to characterize the nanomaterials on all length scales.
Particle size and morphology
Scattering and imaging methods such as line broadening in X-ray diffraction, small angle X-ray and neutron scattering and transmission electron microscopy, are employed to determine average particle and grain size, their distributions and the morphology of the particles. Additionally, nitrogen adsorption, light scattering, atomic probe techniques and mass spectroscopy provide complementary information on these size related parameters. The method of choice depends on the type of material (powder, solid and liquid dispersion, consolidated and sintered ceramic, etc.). Care should be taken in comparing the average sizes determined by these methods because different size related parameters are determined (e.g. column length in XRD line broadening) and the average values are based on different weight functions.