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981.
The perturbation formulae of the spin Hamiltonian parameters (the anisotropic g factors, hyperfine structure constants and superhyperfine parameters) are established for a 5d7 ion in an orthorhombically elongated octahedron based on the cluster approach. These formulae are applied to the theoretical studies of the EPR spectra and the local structures for the tetragonal and orthorhombic Ir2+ centers in AgCl. For the tetragonal Ir2+ center, the uncompensated substitutional [IrCl6]4 cluster is found to experience a relative elongation of about 0.08 Å along the C 4 axis due to the Jahn–Teller effect. For the orthorhombic center, the ligand octahedron also suffers Jahn–Teller elongation (by about 0.08 Å) along the [001] (or Z) axis. Meanwhile, the ligand Cl intervening in the impurity Ir2+ and the next nearest neighbor silver vacancy VAg along the [100] (or X) axis may undergo an inward displacement of 0.004 Å towards the center of the octahedron due to electrostatic repulsion of the VAg. The calculated spin Hamiltonian parameters based on the above local structures show good agreement with experimental data for both centers. 相似文献
982.
In the majority of cases, the effects of ion implantation are confined close to the implant zone but, potentially, the resultant distortions and chemical modifications could catalyse relaxations extending into the bulk substrate. Such possibilities are rarely considered but the present data suggest that high dose ion implantation of ZnO has induced bulk changes. Surface implants with Cu and Tb strongly modified the low temperature bulk thermoluminescence properties generated by X-ray irradiation. Suggestions are proposed for the possible mechanisms for bulk relaxations and structural characteristics, which may indicate where such instability may occur in other lattice structures. 相似文献
983.
An annular interfacial crack between dissimilar piezoelectric layers subjected to electroelastic loadings was investigated under an electrically impermeable boundary condition on the crack surface by using the Hankel transform technique and the Cauchy singular integral equation method. The stress intensity factors and energy release rates were determined. Numerical results reveal the effects of crack configuration, electric loads and material parameters on crack propagation and growth. The results should be useful for the design of piezoelectric composite structures and devices of high performance. 相似文献
984.
Σ3 grain boundaries form as a result of either growth twinning or deformation twinning in face centered cubic (fcc) metals and play a crucial role in determining the mechanical and electrical properties and microstructural stability. We studied the structure and stability of Σ3 grain boundaries (GBs) in fcc metals by using topological analysis and atomistic simulations. Atomistic simulations were performed for Cu and Al with empirical interatomic potentials to reveal the influence of stacking fault energy on the morphology of the twinned grains. Three sets of tilt Σ3 GBs were studied with respect to the tilt axis parallel to ?111?, ?112?, and ?110?, respectively. We showed that Σ3{111} and Σ3{112} GBs are thermodynamically stable and the others will dissociate into terraced interfaces regardless of the stacking fault energy. The morphology of the nano-twinned grains in Cu is predicted from the above analysis and found to match with experiments. 相似文献
985.
Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy were used to study the microstructure evolution of Al–Cu–Mg alloy during the initial stage of homogenization. It was found that two types of precipitation-free zones (PFZs) can form concurrently: one near grain boundaries and the other at the grain centres. Depth profile analyses of solute concentrations and dislocation-loop distributions strongly suggested that the formations of the two type of PFZs are different, due solely and exclusively to solute and vacancy depletion, respectively. A mechanism model was proposed to explain the concurrent formation of the two different type of PFZs during the initial stage of homogenization. 相似文献
986.
Abstract Infrared spectroscopy has been a workhorse technique for materials analysis and can result in positively identifying many different types of material. In recent years there have been reports using wavelet analysis and machine learning algorithms to extract features of Fourier transform infrared spectrometry (FTIR). The machine learning algorithms contain back-propagation neural network (BPNN), radial basis function neural network (RBFNN), and support vector machine (SVM). This article reviews the important advances in FTIR analysis employing a continuous wavelet transform (CWT) and machine learning algorithms, especially in the applications of the method for Chinese medicine identification, plant classification, and cancer diagnosis. 相似文献
987.
The condensation heat transfer characteristic curves for a ternary vapor mixture of water, ethanol, and air (or nitrogen) under several ethanol concentrations and relatively low concentrations of air (or nitrogen) were measured. The effect of non-condensable gas on several different domains in the condensation curves was discussed. The effect of non-condensable gas in the domains controlled by the diffusion resistance and the filmwise condensation was not notable; whereas that in the domain dominated by the condensate resistance of dropwise mode was remarkable. Moreover, variations due to changes in non-condensable gas concentration of several characteristic points representing the curves were discussed. 相似文献
988.
989.
ABSTRACTThe concentration of carbon dioxide (CO2) has a significant influence on the morphology of thermal decomposition products of magnesite. So, structures, stabilities and adsorption mechanisms of (MgO)m (m?=?1–6) clusters by one or two CO2 molecules were calculated by the GGA-PW91 method. The results show that the stability of the considered clusters is (MgO)m(CO2)2 clusters > (MgO)m(CO2) clusters > (MgO)m clusters by the average binding energy. Certain low-lying isomers of (MgO)m(CO2) and (MgO)m(CO2)2 clusters which have an isolated O atom are deviating from the cluster center which possess higher kinetic activity. (MgO)m clusters prefer to adsorb a CO2 molecule, while (MgO)3(CO2) clusters prefer to adsorb a CO2 molecule rather than the neighbors. Magnesite is difficult to transit to (MgCO3)2 clusters at room temperature. However, magnesite will spontaneously transit to (MgO)2 clusters and further transit to MgO crystal which need to adsorb more energy at 700?K. 相似文献
990.
Zhongyuan Huang Renguo Lu Ting Huang Hongyan Wang Tongsheng Li 《Journal of Macromolecular Science: Physics》2013,52(7):937-949
Crosslinked fluorinated polyimides (CFPI) were successfully synthesized to study and explore the effect of cross-linkage on the migration of fluorinated segments and on the adhesion strength. Characterization by dynamic thermomechanical analysis (DMA) and thermo gravimetric analysis (TGA) confirmed good thermal properties of CFPI. X-ray photoelectron spectroscopy (XPS) results showed that the ratio of fluorinated component (6FDA-ODA) concentration of the surface to the bulk decreased with the crosslink density. The water contact angle of CFPI was lower than that of non-crosslinked fluorinated polyimide, indicating that the migration of fluorinated groups to the surface was reduced by the presence of cross-linkage. Therefore, CFPI, with no fluorine segregation on the surface, exhibited excellent wetting of adherent surfaces and adhesion strength, which was proved by lap shear strength (LSS) measurements and scanning electron microscopy. 相似文献