Morphological Crystallography

it is not possible to obtain single crystals that are large enough to be worked with in a convenient manner. In those cases, physical properties must be measured on poly crystalline samples. There is always discrepancy, or disagreement, between measured physical properties of single crystals and polycrystals due to microstructural effects. Hence, physical properties measured from polycrystalline samples are sometimes considered less reliable from a reproducibility standpoint. 

Weiss and Mohs also developed notation systems relating each face to the coordinate axes, but these were surpassed in use by a system first introduced by the British polymath William Whewell (1794-1866) during a crystallography fellowship period in 1825, and later incorporated in an 1839 book by his student William Hallowes Miller (1801-1880). The notation system, now named after Miller, is discussed further in Section 1.3.2. 

Just as there is a correspondence between the symmetry of crystals and that of their physical properties, there is also a connection between the symmetry exhibited by a crystal at the macroscopic and microscopic length scales, in other words, between the external crystal morphology and tme internal crystal structure. Under favorable circumstances, the point group (but not the space group) to which a crystal belongs can be determined solely by examination of 

Crystal Class Symmetry Elements0 Forms Occurring in the Respective Crystal Class Representative Inorganic/Mineral Substances 

C2 Tetragonal pyramid, tetragonal prism, pedion None known 

---

Thus, the interaction of the primary beam with the sample provides a wealth of information on morphology, crystallography and chemical composition. Using transmission electron microscopy to make a projection of the sample density is a routine way to study particle sizes in catalysts. 

Thus, the interaction of the primary beam with the sample provides a wealth of information on morphology, crystallography and chemical composition. 

Keywords SnC>2, nanoparticles, morphology, crystallography, photo-catalytic activity. 

Closely spaced magnetic nanocrystals that are found in nature are often more perfect in their sizes, shapes and arrangements than their synthetic counterparts. As a result, they can be chosen as model systems to study the effect of particle size, morphology, crystallography and spacing on magnetic microstructure. 

Hatiy enunciated the laws governing crystal symmetry, and paved the way for his later discovery of the law of rational indices, which, in 1801, he substantiated by a comprehensive survey of the mineral kingdom. Thus by the first year of the nineteenth century the fundamental laws of morphological crystallography had been established. 

F. Hasan, A. Jahanafrooz, G.W. Lorimer, and N. Ridley, The Morphology, Crystallography, and Chemistry of Phases in As-Cast Nickel-Aluminum Bronze, Metall. Trans. A, Vol 13, 1982, p 1337-1345... 

Spa] Spanos, G., The Morphology, Crystallography, and Mechanism of Carbide Precipitation in an Fe-0.12C-3.28Ni Alloy , Metall. Trans. A, 23A(1), 171-181 (1992) (Experimental, Meehan. Prop., Morphology, 44)... 

Miller indices are important to the crystallisation scientist as they provide a link between the modem structural crystallography of X-ray diffraction and classical morphological crystallography of shape and habit. This allows the process chemist or pharmaceutical scientist to link the internal molecular structure to the chemical functionality of the external surface stracture. Figure 8.2 (bottom right) shows the observed morphology for D-mannitol with the Miller indices labelled. 

---