Crystal strain

Iron, nickel, cobalt, tungsten and chromium do not behave reproducibly due to crystal strain or oxide coatings. Metal electrodes which respond directly to solutions of their own ions are called Class I or first order. ... 

First, it is necessary to eliminate tautomerism or dynamic isomerism by determining that the two materials give identical melts. X-ray diffraction can determine that crystal strain (which can be mistaken for polymorphism) is not a factor. Then, McCrone... 

X-ray powder diffraction the powder patterns for the bundle-like and conventional crystals are shown in Fig. 10.3. They are quite similar, as expected for materials that have essentially the same crystal structure. However, there are some slight differences in the peak positions, which was attributed to the difference in water content and degree of internal crystal strain. There are some more obvious differences in relative intensities, including the position of the strongest peak. There are clear differences in the peak widths, which also reflects differences in the degree of crystallinity ... 

The theory was used to calculate kinetic curves for the polymerization of PTS deducing the ratio cJCp from the known conversion dependence of the lattice parameters. Time conversion curves normalized with respect to the time necessary to reach 50 percent conversion can be calculated for different values of the lattice mismatch using the crystal strain theory. For PTS a satisfactory fit of the experimental data of the thermal and y-ray polymerization can be obtained. However, further studies of the kinetics of the solid-state polymerization of PTS and other monomers provided results which cannot be explained by the theory. 

The small random crystal strains can be quantified and this is also given in Table 5. It was found that the sttain can be described by a Gaussian distribution characterised by a mean value, 8, of zero and a half width of 8a = 2cm . The analysis also differed from that of previous workers in both the hyperfine values and the requirement of a nuclear quadrupole term. The transitions within the lowest excited singlet could also be observed directly [31]. It can be concluded that the Cu(ll)/MgO system can be described as an almost pure dynamic Jahn-Teller case. 

Correspondingly two order parameters are characterizing the system, and the total crystal strain is zero... 

The scenario would envisage that the crystal strain increases in the phenylurethane series such that a blue shift, which is essentially that of the LT to HT transition, would result. The loss of detailed structure occurring on the thermochromic transition to the HT spectrum would result from an extreme increase in disorder which could be mainly attributed to dynamic processes, such as sidechain motions, which are intensified at higher temperatures. A theoretical approach not unlike this has been recently advanced by Schweizer (24). Both weak and strong disorder regimes are considered in that treatment. 

If the stress-strain behaviour after flow has commenced is examined, then we find a law of the form (8.37), the exponent tn determined by Ready and Kingery varying from about 2-5, for crystals strained by less than about 10 per cent, to 1-5 for heavily strained crystals. This latter result agrees well with the creep experiments diseussed above, while the measured activation energy, H = 0 62 o o6 eV, is only slightly smaller. 

Large-angle X-ray powder diffraction (XRD) has been one of the most versatile techniques utilized for the structural characterization of nanocrystalline metal powders. The modern improvements in electronics, computers, and X-ray sources have allowed XRD to become an indispensable tool for identily-ing nanocrystalline phases as well as crystal size and crystal strain. The comparison of the crystallite size obtained by the XRD difffactogram using the Scherrer formula with the grain size obtained from the TEM image allows us to establish if the nanoparticles have a mono- or polycrystalline nature. 

In Fig. 8(a) we show the experimental result of an orientational variation of in the x, y plane of the laboratory frame (see Fig. 8(b)) for 2 different molecules (dots and triangles) together with simulated curves. This experiment was performed in the setup where the sample is mounted at the tip of the hbre. Owing to the induced crystal strain the optical transitions of sites Oi and O2 then overlap and it is impossible to decide to which site a molecule belongs. It is seen that both molecules show a rather different behaviour of the line position as a function of the orientation of Bo. Whereas Mi undergoes a marked change of the ODMR transition frequency, M2 hardly shows any variation. This is a signature for a different orientation of... 

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