Crystals atomic concentration

An alternative, but to some extent complementaty approach to the structure of grain boundaries notes that as the tilt angle between the crystals forming the grain boundary increases, planes of lower atomic concentrations, the high index planes, such as (221), (331) and (115) in the face-centred strucmre, become parallel to the grain boundary. There is therefore a decrease in the number of metal-metal bonds at the boundary as the tilt angle increases. 

The approximate calculation of the surface energies of metals as a function of crystal structure described earlier uses the enthalpy of sublimation, s, and the co-ordination number to calculate the energy as a function of the atomic concentration on the surface. The atomic areas of the principal configurations are as follows ... 

Among the alkali metals, Li, Na, K, Rb, and Cs and their alloys have been used as exohedral dopants for Cgo [25, 26], with one electron typically transferred per alkali metal dopant. Although the metal atom diffusion rates appear to be considerably lower, some success has also been achieved with the intercalation of alkaline earth dopants, such as Ca, Sr, and Ba [27, 28, 29], where two electrons per metal atom M are transferred to the Cgo molecules for low concentrations of metal atoms, and less than two electrons per alkaline earth ion for high metal atom concentrations. Since the alkaline earth ions are smaller than the corresponding alkali metals in the same row of the periodic table, the crystal structures formed with alkaline earth doping are often different from those for the alkali metal dopants. Except for the alkali metal and alkaline earth intercalation compounds, few intercalation compounds have been investigated for their physical properties. 

A possible layered precursor to the layered nanoproduct conversion mechanism is thus proposed. The silver clusters formed at the initial heating stage by the partial decomposition of AgSR serve as nuclei at further reaction stages, and their distribution naturally inherits the layered pattern of the precursor. The following growth is mainly controlled by the atom concentration and atom diffusion path, which are both constrained by the crystal structure of the precursor [9]. 

Another system obeying Fick s law is one involving the diffusion of small interstitial solute atoms (component 1) among the interstices of a host crystal in the presence of an interstitial-atom concentration gradient. The large solvent atoms (component 2) essentially remain in their substitutional sites and diffuse much more slowly than do the highly mobile solute atoms, which diffuse by the interstitial diffusion mechanism (described in Section 8.1.4). The solvent atoms may therefore be considered to be immobile. The system is isothermal, the diffusion is not network constrained, and a local C-frame coordinate system can be employed as in Section 3.1.3. Equation 2.21 then reduces to... 

The diffusion coefficient of D atoms in a D2 crystal (measured in the same way as described above) is also temperature-independent in the range 1.9 to 4.2 K, though it is 4 orders of magnitude smaller than for H in H2 [Lee et al., 1987 Miyazaki et al., 1989], In mixed crystals of D2 and HD (from 20 1 to 7 1) a decrease in the D-atom concentration coincides with an increase in that of H, so that the total concentration remains constant. This means that the conversion is due to the diffusion-limited exchange reaction... 

A B20 crystal field parameter decreases as hydrogen atoms concentration increases (Fig. 6) and, therefore, the rare-earth sublattice magnetic anisotropy constant Kir (K1r -J2B20Bj2(x), where Bj2(x) is the 2nd order generalized Brillouin function) also decreases. Hydrogenation leads to a decrease of the... 

Electrolytic polarization of such an electrode changes primarily the rate of the charge transfer reaction (step 2 or 3) while the rate of step 1 can be altered appreciably only by changes of the concentration of the adsorbed atoms or the half crystal atoms. The reason is that the activation energy of the charge transfer reaction varies with the shift of electrical... 

In Equation (23), and [REEJmeit are atomic concentrations on a six-oxygen basis in crystal and melt phases, respectively. If, as they usually are, the molecular weights of crystal and melt (on a six-oxygen basis) are within a few percent of one another, then the ratio of REE atomic concentrations approximates ... 

Figure 6. A change with time of H- and D-atom concentrations (in arbitrary units) after cutoff of /-irradiation of mixed crystal Dj-HD (15.6 mol %) at 4.2 K determined by the reaction HD -I- D- H -I- Dj.

Crystals develop faces in a manner that depends on the internal structure of the crystal, the concentration of atoms on a face, and the relative rate of growth of that face. 

Summing up what has been described above, the maximum transition temperatures observed for the additive elements Y and La occur at a valence electron per atom of 3.7, and for Ho, Er, Lu and Sc this is 3.9. Cooper et al. (1970) have demonstrated that a new peak of the superconducting transition temperatures exists at the general valence electron per atom concentration of 3.7 to 3.9 for a number of crystal structures of which the PU2C3 structure is one. 

Gerischer made an experimental attempt to measure the crystallization overvoltage of Ag deposition in a chronopotentiometric experiment. In this experiment two results were obtained. From the slope at t -> 0 the capacitance was determined. This capacitance was much larger than the double-layer capacitance and was interpreted as adsorption capacitance Qd- The ad-atom concentration was calculated from the adsorption capacitance... 

This equation means that the chemical potential of atoms in a crystal is dependent on the pressure and the atomic concentration. It is also noted that if the concentration of the vacancy is suflhciendy low, the last term on the right-hand side of Eqs. (5.72) and (5.74) can be neglected. 

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