材料期刊网

EFFECTS OF HIGH TEMPERATURE PRETREATMENTS ON HIGH TEMPERATURE FRACTURE BEHAVIOR OF SiC-C／SiC

X.G.Luan , L.F.Cheng , S.R.Qiao , J.Zhang

金属学报(英文版)

The samples made from a SiC-C/SiC composite were pretreated in Ar under creep, fatigue, creep and fatigue interaction, as well as in dry oxygen and wet oxygen under fatigue at 1300℃ for 15 hours, The fracture behaviors of the pretreated samples were investigated at 1300℃. The loading-strain curves and the microstructures of the sample were compared with each other. The various of high temperature tensile behaviors was attributed to the different microstructures resulted from different high temperature pretreatments.

关键词: C/SiC , null , null

Explanations of the optical spectra and g factor for V3+ ions in ZnX (X = S, Se, Te) crystals

Physica B-Condensed Matter

This paper presents a cluster approach for the calculations of the absorption band positions and the g factor of d(2) tetrahedral cluster. In the approach, the different modifications of e and t(2) orbitals of d electrons and the contribution from the spin-orbit coupling of ligands to the EPR g factor due to the mixing of d(2) ions with the ligands are considered. The calculated band positions and g factor for ZnX : V3+ (X = S, Se, Te) crystals show good agreement with the observed values by using only two adjustable parameters. The contribution from the spin-orbit coupling of ligands to the g factor is discussed. (C) 1998 Elsevier Science B.V. All rights reserved.

关键词: crystal- and ligand-field theory;optical spectra;electron paramagnetic;resonance;spin-orbit coupling;V3+ ZnX (X = S, Se, Te);vanadium centers;znte crystals

INVESTIGATIONS ON THE g FACTORS AND THE SUPERHYPERFINE PARAMETERS FOR THE TETRAGONAL Pd(3+) CENTERS IN AgX (X = Cl, Br)

International Journal of Modern Physics B

The g factors and the superhyperfine parameters for the tetragonal Pd(3+) centers in AgX (X = Cl, Br) are theoretically investigated from the perturbation formulas of these parameters for a 4d(7) ion in tetragonally elongated octahedra In the calculations, the related molecular or coefficients and the unpaired spin densities of the ligands are determined quantitatively from the cluster approach in a uniform way. Both centers originate from substitutional Pd(3+) on Ag(+) site in AgX, with no charge compensator (silver vacancy) nearby. The [PdX(6)](3-) clusters suffer a relative elongation of 0.01 angstrom (or 0.06 angstrom) along [1 0 0] (or C(4)) axis for X = Cl (or Br) due to the Jahn-Teller effect The calculated g factors and the superhyperfine parameters based on the above Jahn-Teller elongations show good agreement with the experimental data.

关键词: Electron paramagnetic resonance;crystal and ligand fields;Pd(3+);AgCl;AgBr;transition-metal ions;epr spectroscopic investigations;electron-paramagnetic-resonance;atomic screening constants;laser-light;generation;color image-formation;silver bromide;superposition model;scf functions;agbr

Theoretical investigations of the g factors and the local structure for the trigonal Zr(3+) center in X-ray irradiated YSZ

Journal of Alloys and Compounds

The electron paramagnetic resonance (EPR) g factors g(parallel to) and gperpendicular to and the local structure for the trigonal Zr(3+) center in X-ray irradiated yttria-stabilized zirconia (YSZ) are theoretically investigated from the perturbation formulas of the g factors for a 4d(1) ion in trigonally distorted octahedra. Based on the studies, in this trigonal center (characterized as [ZrO(6)](9-) cluster associated with two oxygen vacancies V(o) along the [ 111] axis), the O(2-) ions in the ligand triangles are found to displace towards the neighbouring Vo by about 0.42 Angstrom due to the electrostatic attraction of the V(o). The above displacement is comparable with that (approximate to 0.36 Angstrom) obtained from neutron diffraction measurements and those (approximate to 0.24-0.37 Angstrom) based on the optical spectral analysis and crystal-field calculations in the previous works. Particularly, partial quenching of the spin-orbit (SO) coupling interaction (i.e., gamma(SO) approximate to 0.44) due to the dynamic Jahn-Teller effect (DJTE) and its influence on the g factors, which were ignored by the previous authors, are taken into account in the present work. The validity of the results is discussed. (C) 2004 Elsevier B.V. All rights reserved.

关键词: electron paramagnetic resonance (EPR);defect structure;crystal-fields;and spin Hamiltonian;Zr(3+);yttria-stabilized zirconia (YSZ);oxide fuel-cells;paramagnetic-resonance spectra;yttria-stabilized;zirconia;spin-orbit interaction;single-crystals;electron traps;ions;epr;fabrication;impurity

Calculation of EPR parameters g factors for Ce3+ ion in YBa2Cu3O6+x superconductor

International Journal of Modern Physics B

The perturbation formulae of EPR parameters g factors g(x), g(y) and g(z) for the lowest Kramers doublet of 4f(1) ion in orthorhombic symmetry are established. In these formulae, the contributions of the covalency effects, the admixture between J = 7/2 and J = 5/2 states as well as the second-order perturbation (which is not considered in the previous works) via crystal-field and orbital angular momentum interactions are all included. According to these formulae, and by using the superposition model, the g-factors g., g(y) and g(z) for Ce3+ center in YBa2CU3O6+x superconductor are calculated. The results are discussed.

关键词: YBa2Cu3O6+x;EPR;superposition model;Ce3+;crystal-field

PVC／PP-g-MAH共混物X射线能谱微区分析

赵敏 , 姚子华 , 张荣珍 , 高俊刚

高分子材料科学与工程

用X射线能谱微区分析方法对PVC／PP-g-MA H共混物进行了研究,得到了共混物断面氯元素的面分布图,并对面分布图像进行了相分析,从 亚微观层次揭示了PVC／PP-g-MAH共混物的相结构。通过对元素面分布图的面积计算,研究 了共混组成与相容性的关系,并初步探讨了共混物力学性能与面分布的相关性。

关键词: X射线能谱 , 微区分析 , 面分布 , 相结构 , PV C/PP-g-MAH

Investigations of the g factors for the orthorhombic Co2+ center in YBa2Cu2.7Co0.3O7-x at room temperature

Physica C-Superconductivity and Its Applications

The anisotropic g factors g(x), g(y) and g(z) for the orthorhombic Co2+ center on the Cu(l) site in YBa2Cu2.7CO0.3O7-x at room temperature are theoretically investigated from the perturbation formulae of the g factors for a 3d(7) ion having low spin (S = 1/2) under octahedra with orthorhombic distortion. In these formulae, the contributions to the g factors from the orthorhombic crystal-fields as well as the ligand orbitals and spin-orbit coupling are taken into account based on the cluster approach. This center may be attributed to Co2+ located in a moderately compressed oxygen octahedron with additional orthorhombic distortion. The significant decline (characterized by the reduction factor y approximate to 0.13) of the energy separations due to the Jahn-Teller effect is suggested, by analyzing the experimental g factors. The calculated g factors based on the above contributions show good agreement with the observed values. In addition, the pronounced decrease in the intensity and the remarkable nonlinear increase in the g, of Co2+ EPR spectra as the temperature is lowered from room temperature to 150 K are also mentioned, in view of the opening of the spin gap due to antiferromagnetic interactions. (c) 2007 Elsevier B.V. All rights reserved.

关键词: electron paramagnetic resonance;crystal fields and spin hamiltonians;Co2+;YBa2Cu2.7Co0.3O7-x;atomic screening constants;d-orbital theory;paramagnetic-resonance;scf functions;spin gap;field;ions;0-less-than-or-equal-to-x-less-than-or-equal-to-0.30;yba2cu3o7-delta;la2-xsrxcuo4

Investigations on the EPR g factors for the six-coordianted Cu2+(1) site in YBa2Cu3O6+x

International Journal of Modern Physics B

The EPR g factors g(//) and g(perpendicular to) for the six-coordinated Cu2+(1) site in YBa2Cu3O6+x are theoretically investigated from the perturbation formulas for a 3d(9) ion in tetragonally elongated octahedra. The related tetragonal crystal-field parameters Ds and Dt are determined from the superposition model and the structural data for the Cu2+(1) site, by considering the effective elongation of the oxygen octahedron due to the Jahn-Teller effect of the Cu2+ cluster. Based on the calculations, the effective elongation (= 15%) of the ligand octahedron is obtained for the signals at 100K. As for the EPR signals at room temperature, the elongation declines to merely 4%, corresponding to the smaller anisotropy Delta g (=g(//) - g(perpendicular to)). The theoretical results for the g factors are in good agreement with the observed values, and the local tetragonal distortion due to the Jahn-Teller effect is discussed.

关键词: crystal fields and spin hamiltonians;electron paramagnetic resonance;Cu2+;YBa2Cu3O6+x;single-crystals;yba2cu3o7-delta;evolution;esr

Investigation of the EPR g factors and defect structure for the Cu2+-V-Na center in the X-irradiated NaCl: Cu+ crystal

Physica B-Condensed Matter

The g factors of a tetragonally-compressed Cu2+ center in NaCl: Cu+ crystal X-irradiated at room temperature are calculated from the high-order perturbation formulas based on the two-mechanism model. In the model, the contribution to g factors from both crystal-field (CF) and charge-transfer (CT) mechanisms are included. The calculations are based on the defect model that the tetragonally-compressed Cu(2+)center is assigned to the Cu2+ ion (which is caused by Cu+ ion (at the Na+ site) irradiated by X-ray) associated with a nearest Na+ ion vacancy V-Na along C-4 axis due to charge compensation. From the calculations, the g factors g(parallel to) and g(perpendicular to) are explained and the defect structure (charactering by the displacement Delta Z of the Cl- ion intervening in Cu2+ and V-Na) of the Cu2+ (or Cu2+-V-Na) center is obtained. The results are discussed. (C) 2011 Elsevier B.V. All rights reserved.

关键词: Electron paramagnetic resonance (EPR);Defect structure;Crystal- and;ligand-field theory;NaCl;Cu2+;spin-hamiltonian parameters;jahn-teller;single-crystals;cu2+;ions;resonance;spectrum;ligand;temperature;transitions

Investigations of EPR g Factors and Rhombic Distortion for the Rhombic Cu2+ Centers in K2Zn1-x Cu (x) F-4 Crystals at Low Temperature

Applied Magnetic Resonance

The electron paramagnetic resonance g factors g (i) (i = x, y, z) of two rhombic Cu2+ centers, Cu2+(II) and Cu2+(III), in K2Zn1-x Cu (x) F-4 crystals found at low temperature are calculated from the complete diagonalization (of energy matrix) method based on the cluster approach. The calculations show that the ground state wave function of the two rhombically compressed Cu2+ centers is with a small admixture of . The rhombic distortions for both Cu2+ centers are obtained from the calculations. The results are discussed.

关键词: electron-paramagnetic-resonance;atomic screening constants;hyperfine;parameters;gyromagnetic factor;spin resonance;scf functions;field;copper(ii);dependence;spectra