Intergrain boundary

Provided that real polycrystalline samples are subject of a spatially non-homogeneous distribution of traps near the sample surface and within intergrain boundaries, the pretransit time averaged carrier flux is composed of two comparable parts one due to usual carrier drift in the external field and the second due to carrier diffusion [see Eq. (198) and Sec. 4.4] ... 

When fluorine is incorporated into a sample with a low zirconium content, the integral density of extended defects remains nearly constant, although the relative share of defects assigned to intergrain boundaries somewhat increases. 

TEM data (not shown for brevity) revealed the samples particles to be of a platelet appearance, with the most developed faces being of (111) and (110) types as determined by SED analysis. Intergrain boundaries are present in low surface area samples. 

The simple model implies an infinite perfect crystal. The crystal specimen studied is necessarily finite (rarely more than 0.5 mm in size) and, if perfect by conventional criteria, would be utterly unsuitable for collection of intensity data of the kind required for ordinary structure determination and refinement. What is needed is an ideally imperfect crystal shot through with dislocations and intergrain boundaries so that it behaves, so far as diffraction is concerned, like a mosaic of perfect crystal blocks of the order of micrometers or tenths of micrometers in size, tilted with respect to one another by angles of the order of a few seconds of arc and scattering independently (incoherently) with respect to one another. The assumption of an ideally imperfect ... 

Fig. 6.13. Close-up STM image of the intergrain boundary showing the interlacing of the grains.

Adsorption of these ions (as well as some organic molecules) hampers surface recombination and/or recombination at the intergrain boundaries in the polycrystalline samples [9, 22, 23]. Incidentally, special "texturizing" etching of the surface [8, 9] is used to make surface "matt" and thus reduce its reflectivity. 

Special activity is often attributed to lattice defects such as dislocations, kinks, vacancies, stacking faults, and intergrain boundaries emerging at the crystal surface. Experiments carried out with catalysts containing different numbers of defects have shown, however, that it will not be justified to identify crystallographic defects emerging at the electrode surface with the active sites responsible for catalytic activity of the electrode as a whole. 

This phenomenon (see the report of Merino, these lectures) has been modeled using equations of pressure solution coupled to the transport of solute species along intergrain boundaries [ 6, ] The central approach was to consider any given crystal to evolve in an average environment specified by the local texture. Consider a crystal of ijineral i of volume L (r,t) and located in the vicinity of point r L is taken to evolve according to... 

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