Polycrystalline structure/morphology

Equation (5.75) is of great usefulness, above all, when discussing grain morphology within a polycrystalline structure. If the orientation dependence of 7 is ignored, it says that for a contact of three grains the equilibrium angle is 120° and for a contact... 

In summary, large (>lpm) single crystal platelets of aurichalcite produced highly dispersed Cu and ZnO particles with dimensions on the order of 5 nm, as a result of standard catalyst preparation procedures used in the treatment of the precipitate precursors. The overall platelet dimensions were maintained throughout the preparation treatments, but the platelets became porous and polycrystalline to accommodate the changing chemical structure and density of the Cu and Zn components. The morphology of ZnO and Cu in the reduced catalysts appear to be completely determined by the crystallography of aurichalcite. 

Thin films of metals, alloys and compounds of a few micrometres thickness, which play an important part in microelectronics, can be prepared by the condensation of atomic species on an inert substrate from a gaseous phase. The source of the atoms is, in the simplest circumstances, a sample of the collision-free evaporated beam originating from an elementary substance, or a number of elementary substances, which is formed in vacuum. The condensing surface is selected and held at a pre-determined temperature, so as to affect the crystallographic form of the condensate. If this surface is at room temperature, a polycrystalline film is usually formed. As the temperature of the surface is increased the deposit crystal size increases, and can be made practically monocrystalline at elevated temperatures. The degree of crystallinity which has been achieved can be determined by electron diffraction, while other properties such as surface morphology and dislocation structure can be established by electron microscopy. 

The underpotential deposition (UPD) of metals on foreign metal substrates is of importance in understanding the first phase of metal electrodeposition and also as a means for preparing electrode surfaces with interesting electronic and morphological properties for electrocatalytic studies. The UPD of metals on polycrystalline substrates exhibit quite complex behavior with multiple peaks in the linear sweep voltammetry curves. This behavior is at least partially due to the presence of various low and high index planes on the polycrystalline surface. The formation of various ordered overlayers on particular single crystal surface planes may also contribute to the complex peak structure in the voltammetry curves. 

As noted in Fig. 14.1 (a), commercial fibers of semicrystallme polymers are always cold-drawn after spinning to achieve further structuring through further macromolecular orientation and crystalline morphological changes, many of which are retained because of the low temperature of the cold-drawing processes. A typical stress-strain curve for a polycrystalline polymer at a temperature Tg < T < Tm appears in Fig. 14.6. 

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