Site disorder

Chandler, R. E. Houtepen, A. J. Nelson, J. Vanmaekelbergh D. 2007. Electron transport in quantum dot solids Monte Carlo simulations of the effects of shell filling, Coulomb repulsions, and site disorder. Phys. Rev. B 75 085325-085335. 

Armbruster T. and Geiger C. A. (1993). Andradite crystal chemistry Dynamic X-site disorder and structural strain in silicate garnets. Eur. J. Min., 5 59-71. 

Injection site reaction Application site disorders 31,302 0.9... 

An alternative model [22] favours a uniform B-site disorder extending throughout the volume and consisting of local clusters of ferroelectric and antiferroelectric ordering with the highly polarizable Pb ion almost certainly playing an important role. 

Second, the use of meshed particles versus a pressed wafer will typically lead to nonuniformity of X-ray absorption thickness. This can be directly observed by placing an X-ray sensitive camera behind the sample a sample of a powder pressed into a wafer is spectroscopically more uniform than a catalyst bed of meshed particles. Naturally the contrast becomes more extreme as the meshed particles become larger. Moreover, if the sample is spatially nonuniform then severe constraints are placed on the positional stability of the X-ray beam. Any motion of the position of the X-ray beam will then probe different thicknesses of the sample, with direct consequences on the measured S/N. From the perspective of XAFS spectroscopy, any nonuniformity of the sample thickness could directly affect the accuracy of the measurement of the amplitude of the X-ray absorption coefficient. It is the amplitude that contains information about the coordination number and site disorder. As has been discussed elsewhere (Koningsberger and Prins, 1988), these amplitude distorting effects are given the general heading of "thickness effects." In brief, a thickness effect occurs when part of the incident X-ray beam is not attenuated by the sample. In the case of meshed particles this would be in the form of pinholes in the sample. 

A cp/mas VACP 13C-NMR study was made of these three pseudopolymorphic crystals (19, 21, and 22).29 The prefix pseudo is affixed to polymorph to describe this series of nefopam methohalide crystals since the anions therein are different. The results of this solid-state 13C-NMR study are presented in Table 3 along with the solution-state 13C chemical shifts. The cp/mas 13C-NMR spectra of crystalline 19, 21, and 22 are illustrated in Fig. 5. It is seen that the C(4) peak (<5 58.51) in the cp/mas 13C-NMR spectrum of the methochloride (22) is sharp due to the sole presence of the immobile BB conformation quaternary ammonium cation in the crystal. However, the C(4) peak (V) 59.42) in the methobromide (21) spectrum was markedly lower in intensity and broad, and in the methiodide (19) spectrum it was just a broad shoulder at 5 62.29 Therefore, as the C(4) nucleus becomes more site-disordered in the crystal due to conformational interconversion, its cp/mas peaks show lower intensities and greater line-broadening. 

The 30 successive packing calculations consumed, respectively for zeolite Li-A(BW) and zeolite 4A, some 3s and 12s on a workstation, with each structure optimization then reqmring an additional 2 or 8 min. respectively. In the latter case, in which the local structure provided by the simulations and the sample-averaged structure yielded by difiraction differ, the modeling results also allow the local effects of the site disorder to be explored. These encouraging results set the stage for extensions to still more complex systems and to structures for which less direct experimental data are available. 

Effect of A-site Disorder and Cation Radius on D(T i) and Tco- The effect of changing the contents of the A-site on the various transition temperatures of interest, Tc (Curie temperature for ferromagnetism), which is generally the same as Tmi (the metal/insulator transition temperature) and Tco (the charge ordering transition temperature), can be quite large as in Figure 26 Attfield was able to show that Tc(Tmi) correlated very well with the statistical variance, a, of the A-site ions, that is, a = Ily,r — (rA). Here the r, are the standard Shannon radii for 9-fold t coordination, y,... 

Indium Antimonide. Among the binary semiconductors, InSb has received extensive attention in the experimental and theoretical studies due to the complex transition mechanisms involved in its high-pressure behavior [165]. The traditional phase diagram in InSb [166] was substantially revised recently [167, 168]. Two high-pressure phases of InSb are the site-ordered orthorhombic Cmcm and Immm structures, the transition between which proceeds via an intermediate site-disordered orthorhombic phase with Imma symmetry [167]. At room temperature, the transition sequence in InSb depends on the pressurization rate. At slow loading, zincblende strucmre transforms into Cmcm at 2 GPa, whereas rapid loading rates lead to a direct zincblende Immm transition at 3 GPa [167]. The zincblende Cmcm transformation seems to be reversible and the phases other than zincblende have not been observed at ambient conditions in InSb. 

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