Solid crystalline materials

Bravais lattice — used to describe atomic structure of crystalline -> solid materials [i,ii], is an infinite array of points generated by a set of discrete translation operations, providing the same arrangement and orientation when viewed from any lattice point. A three-dimensional Bravais lattice consists of all points with position vectors R ... 

Grain boundaries — are the interfaces between crystals or individual grains in poly crystalline solid materials. In a simplest case, the grain boundary separates... 

Oxidizer. The major component, by weight and volume, of composite solid propellants is the oxidizer. By far, the most important oxidizer used is AP, a crystalline solid material ground to exacting particle size distributions. This chemical possesses the desirable properties of high density, good thermal stability, and oxygen availability, and relatively low reactivity and cost. Properties of AP and several other materials that are used as oxidizers are summarized in Table 37.5. 

In the case of crystaUine sohds, more than one equivalent structural unit may be present in the primitive cell. This results in sphttings of the fundamental vibrational modes of these units. In the case of many crystalline solid materials covalent units (e.g. oxo-anions for oxo-salts) are present, together with other groups bonded by ionic bonds (e.g. the cations in the oxo-salts). According to the above group approximation, the internal vibrations of the covalent units can be considered separately from their external vibrations hindered rotations and translations of the group that finally contribute to the lattice vibrations and to the acoustic modes of the unit cell) and those of the other units. The presence of a number of covalent structural units in the primitive cell, causes their internal modes to spHt... 

There are no additional parameters required for implementation of the equations above if all of the sorbent material is able to participate in the formation of the solid solution. However, an additional parameter is required if only a fraction of the sorbent phase can participate in the solid solution. In the case of a crystalline solid material, this parameter is expected to be a small fraction of the total solid added to the system, accounting for the fact that only the surface and some of the first few layers of the sorbent will participate in the formation of a solid solution with the co-precipitating metal ion. The value chosen for this parameter is likely to depend on the dissolution properties of the sorbent and can be considered a fitting parameter. 

Single-crystal X-ray diffraction is the most powerful technique for the detailed structural analysis of crystalline solid materials, and so it finds widespread use in coordination chemistry. It is a mature experimental technique, and the basic principles have been well known for almost a century. Nevertheless, the subject has constantly developed throughout its history, and there have been very significant advances in the last decade or two of the twentieth century. These developments and their exploitation will be the main focus of this section. Background theory and its application in general is described in many standard texts, including some relatively simple treatments. ... 

Amorphous solid Crystalline solid Materials science Polycrystalline sohd Solid state Section 15.8 Covalent network sohd Ionic crystal Metallic crystal Molecular crystal... 

Figure 7.4 shows an initial nonuniform distribution of element i in a medium of j. Atoms of species i diffuse from the region of high concentration to the region of low concentration and establish a more imiform concentration distribution of the species. Self-diffusion also takes place in a relatively pure crystalline solid material controlled by a process known as vacancy mechanism or the hopping process. The ion transport in crystalline electrolyte is controlled by this vacancy diffusion or hopping diffusion mechanism. In this... 

The three-dimensional synnnetry that is present in the bulk of a crystalline solid is abruptly lost at the surface. In order to minimize the surface energy, the themiodynamically stable surface atomic structures of many materials differ considerably from the structure of the bulk. These materials are still crystalline at the surface, in that one can define a two-dimensional surface unit cell parallel to the surface, but the atomic positions in the unit cell differ from those of the bulk structure. Such a change in the local structure at the surface is called a reconstruction. 

Hare D E, Franken J and DIott D D 1995 A new method for studying picosecond dynamics of shocked solids application to crystalline energetic materials Chem. Phys. Lett. 244 224... 

For tire purjDoses of tliis review, a nanocrystal is defined as a crystalline solid, witli feature sizes less tlian 50 nm, recovered as a purified powder from a chemical syntliesis and subsequently dissolved as isolated particles in an appropriate solvent. In many ways, tliis definition shares many features witli tliat of colloids , defined broadly as a particle tliat has some linear dimension between 1 and 1000 nm [1] tire study of nanocrystals may be drought of as a new kind of colloid science [2]. Much of die early work on colloidal metal and semiconductor particles stemmed from die photophysics and applications to electrochemistry. (See, for example, die excellent review by Henglein [3].) However, the definition of a colloid does not include any specification of die internal stmcture of die particle. Therein lies die cmcial distinction in nanocrystals, die interior crystalline stmcture is of overwhelming importance. Nanocrystals must tmly be little solids (figure C2.17.1), widi internal stmctures equivalent (or nearly equivalent) to drat of bulk materials. This is a necessary condition if size-dependent studies of nanometre-sized objects are to offer any insight into die behaviour of bulk solids. 

Acetamide is thus obtained as a colourless crystalline solid, which has a characteristic odour of mice, stated to be due to the presence of small quantities of methylacetamide, CH3CONHCH3. The acetamide can be purified and rendered odourless by re-crystallisation from acetone, and then has m.p. 82°, b.p. 223°. If this recrystallisation is contemplated, the distilled material should be collected directly into a small weighed beaker or conical flask, so that the solidified acetamide can be readily broken up and removed. 

Mix 6 2 ml. (6 4 g.) of pure ethyl acetoacetate and 5 ml. of pure phenylhydrazine in an evaporating-basin of about 75 ml. capacity, add 0 5 ml. of acetic acid and then heat the mixture on a briskly boiling water-bath (preferably in a fume-cupboard) for I hour, occasionally stirring the mixture with a short glass rod. Then allow the heavy yellow syrup to cool somewhat, add 30-40 ml. of ether, and stir the mixture vigorously the syrup may now dissolve and the solution shortly afterwards deposit the crystalline pyrazolone, or at lower temperatures the syrup may solidify directly. Note. If the laboratory has been inoculated by previous preparations, the syrup may solidify whilst still on the water-bath in this case the solid product when cold must be chipped out of the basin, and ground in a mortar with the ether.) Now filter the product at the pump, and wash the solid material thoroughly with ether. Recrystallise the product from a small quantity of a mixture of equal volumes of water and ethanol. The methyl-phenyl-pyrazolone is obtained... 

Below Tg the material is hard and rigid with a coefficient of thermal expansion equal to roughly half that of the liquid. With respect to mechanical properties, the glass is closer in behavior to a crystalline solid than to a... 

Solid-State Lasers. Sohd-state lasers (37) use glassy or crystalline host materials containing some active species. The term soHd-state as used in connection with lasers does not imply semiconductors rather it appHes to soHd materials containing impurity ions. The impurity ions are typically ions of the transition metals, such as chromium, or ions of the rare-earth series, such as neodymium (see Lanthanides). Most often, the soHd material is in the form of a cylindrical rod with the ends poHshed flat and parallel, but a variety of other forms have been used, including slabs and cylindrical rods with the ends cut at Brewster s angle. 

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