Crystal structure changes

This is shown in the following diagram. Note that a simple shift in unit cell dimension is all that is required for the crystal structure change to take place. 

O. Ito and T. Fujiwara, Electronic Structure Analysis of Intermetallics for Crystal Structure Changes in Nb3Al, Modelhng Simul. Mater. Sci. Eng., 2, 363 (1994). 

In relatively recent years, it has been found that that indentations made in covalent crystals at temperatures below their Debye temperatures often result from crystal structure changes, as well as from plastic deformation via dislocation activity. Thus, indentation hardness numbers may provide better critical parameters for structural stability than pressure cell studies because indentation involves a combination of shear and hydrostatic compression and a phase transformation involves both of these quantities. 

Figure 9 shows a spectrum of the hydrolyzed membrane, and peaks appeared at 11, 20, and 22 degrees. The crystal structure changed to that of cellulose II type. 

This class of smart materials is the mechanical equivalent of electrostrictive and magnetostrictive materials. Elastorestrictive materials exhibit high hysteresis between strain and stress (14,15). This hysteresis can be caused by motion of ferroelastic domain walls. This behavior is more complicated and complex near a martensitic phase transformation. At this transformation, both crystal structural changes induced by mechanical stress and by domain wall motion occur. Martensitic shape memory alloys have broad, diffuse phase transformations and coexisting high and low temperature phases. The domain wall movements disappear with fully transformation to the high temperature austentic (paraelastic) phase. 

X-ray diffraction (RIGAKU D MAX/RB, Japan) is used to test the fresh and two used catalysts. Compared with the fresh catalyst, no obvious crystal structure change of the used catalysts is found. 

Yoshikawa, S. et al. (1998). Redox-Coupled Crystal Structural Changes in Bovine Heart Cytochrome c Oxidase. Science 280 1723. 

Yoshikawa, S., Shinzawa-ltoh, K., Nakashima, R., Yaono, R., Yamashita, E., Inoue, N., Yao, M., Fei, M. J., Peters Libeu, C., Mizushima, T., Yamaguchi, H., Tomizaki, T., and Tsukihara, T., 1998, Redox-coupled crystal structural changes in bovine heart cytochrome c oxidase. Science 280 1723nl729. 

A thermodynamic quantity that is a measure of the disorder or randomness in a system. For example, a crystal structure changing to a liquid is associated with an increase in entropy as, for example, the melting of ice crystals forming water under standard conditions. Entropy increases for a spontaneous process. S refers to entropy values in standard states of substances. 

The crystal structure change associated with the solid-state transformation of pure MoFe, i.e., body-centered cubic above the transformation to orthorhombic below it, is analogous to the cubic-to-orthorhombic transformation reported (20) for the 5d hexafluorides, WFe, ReFe, OsFe, IrFe, and PtFe. Another investigation has shown that the solid-state transformation in MoFe involves the crystal structure change from body-centered cubic to orthorhombic see Ref. 14). 

C)n these grounds, we expect templating species to be of critical importance to the formation of particular structures. As the nature and coordination of the template are varied, the resulting crystal structure changes. The geometry of TFS need not be confined to periodic hyperbolic surfaces, although these are responsible for the characteristic zeolite structures, containing arrays of tunnels. 

Ogawa, K., Kasahara, Y., Ohtani, Y. and Harada, J. (1998). Crystal structure change for the thermochromy of N-salicylideneanilines. The first observation by X-ray diffraction. J. Am. 

Figure 3.4.10 Crystal structure change on C02 gas adsorption by [Rh (I l)2(bza)4(pyz)]. The slippage of the 1 D chains and the tilting of the benzene rings were observed during ct—(3 host crystal phase transition.

Ammonium Nitrate. Ammonium nitrate became an important fertilizer after World War II when chemical plants that had been producing munitions were converted to the manufacture of fertilizer. It has a high concentration of nitrogen (35%) which is immediately available to the plant in the form of nitrate. However, ammonium nitrate is hygroscopic and prone to have large density fluctuations with crystal structure changes at 32°C. Ammonium nitrate is explosive if stored improperly. Proper storage methods and safety considerations must be employed. 

The above mentioned prograde series are characterized by the following mineral or crystal structural changes ... 

The substance may undergo a crystal-structure change, such as iron Tiron This is really a phase change but is not as obvious as those shown above. 

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