Crystalline materials single crystals

It is important to keep in mind that the precipitate from a solution is often a mixture of different materials single crystals (that may or may not be a unique crystalline species), polycrystalline powder (which may or may not correspond to one of the single crystals) and amorphous material in varying amount. In the case of a unique single-crystal species and of a powder, it is often sufficient to compare the measured powder diffractogram with that calculated on the basis of the... 

In addition to identifying and characterizing known crystalline phases, single crystal, and more recently, powder diffraction methods can be used to determine the atomic positions within the crystal structures of new and uncharacterized materials. An excellent demonstration of how XRD structure determination methods can be applied in concert with other characterization techniques for... 

There are two broad applications of X-rays in the characterization of materials (i) X-ray spectrometry and (ii) X-ray diffractometry. The former technique is used for chemical analysis and has found only limited use in the characterization of pharmaceuticals. On the other hand, X-ray diffractometry, by providing a means for the study of the structure of crystalline materials, is extensively used to characterize pharmaceutical solids. There are two principal applications of X-ray diffractometry. X-ray crystallography is concerned with the structure determination of crystalline phases. Single crystals are usually used for this purpose. On the other hand, in X-ray powder diffractometry, the sample is usually in the form of a powder. X-ray powder diffractometry is recognized as a powerful technique for the identification of crystalline phases. The technique can also be used for the quantitative analyses of solids. This article will be restricted to the principles and applications of X-ray powder diffractometry (XRD) in the characterization of pharmaceutical solids. 

The TCE of most ceramics is isotropic, although for certain crystalline or single-crystal ceramics, the TCE may be anisotropic, and some may even contract in one direction and expand in the other. Ceramics used for substrates do not generally fall into this category, as most are mixed with glasses in the preparation stage and do not exhibit anisotropic properties as a result. The temperature coefficient of expansion of several ceramic materials is shown in Table 4.5. This parameter is linear over the temperature range of interest. 

DCH polymerized thermally has a fibrous texture and is not single crystalline. When single crystal poly-DCH, prepared by gamma radiation, is exposed to SbX (X = F, Cl), the resultant materials... 

Analytical x-ray instruments ate used to characterize materials in several different ways. As with medical x-ray instmments there are analytical instmments that can produce images of internal stmctures of objects that are opaque to visible light. There are instmments that can determine the chemical elemental composition of an object, that can identify the crystalline phases of a mixture of soHds, and others that determine the complete atomic and molecular stmcture of a single crystal. These ate the most common appHcations for x-ray iastmments. 

The complete characterization of a particulate material requires development of a functional relationship between crystal size and population or mass. The functional relationship may assume an analytical form (7), but more frequentiy it is necessary to work with data that do not fit such expressions. As such detail may be cumbersome or unavailable for a crystalline product, the material may be more simply (and less completely) described in terms of a single crystal size and a spread of the distribution about that specified dimension. 

Commercially available PV systems most often include modules made from single-crystal or poly-ciystalline silicon or from thin layers of amoiphous (non-crystalline) silicon. The thin-filni modules use considerably less semiconductor material but have lower efficiencies for converting sunlight to direct-current electricity. Cells and modules made from other thin-filni PV materials such as coppcr-indiuni-diselenide and cadmium telluride are under active development and are beginning to enter the market. 

The glass membrane of the electrodes discussed above may be replaced by other materials such as a single crystal or a disc pressed from finely divided crystalline material it may be advantageous to incorporate the crystalline material into an inert carrier such as a suitable polymer thus producing a heterogeneous-membrane electrode. 

The next step is the hydrogen reduction of the trichlorosilane (Reaction 2 above). The end product is a poly crystalline silicon rod up to 200 mm in diameter and several meters in length. The resulting EGS material is extremely pure with less than 2 ppm of carbon and only a few ppb of boron and residual donors. The Czochralski pulling technique is used to prepare large single crystals of silicon, which are subsequently sliced into wafers for use in electronic devices.1 1... 

Single-Crystal Silicon. Silicon is still the dominant material in photovoltaic. It has good efficiency, which is 25% in theory and 15% in actual practice. Silicon photovoltaic devices are made from wafers sliced from single crystal silicon ingots, produced in part by CVD (see Ch. 8, Sec. 5.1). However, silicon wafers are still costly, their size is limited, and they cannot be sliced to thicknesses less than 150 im. One crystalline silicon wafer yields only one solar cell, which has an output of only one watt. This means that such cells will always be expensive and can only be used where their high efficiency is essential and cost is not a major factor such as in a spacecraft applications. 

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