材料期刊网

搅拌摩擦加工细晶AZ91镁合金的加工特性

G.V.V.SURYAKIRAN , K.HARIKRISHNA , Sk.SAMEER , M.BHARGAVI , B.SANTOSHKUMAR , G.MOHANARAO , Y.NAIDUBABU , RAVIKUMARDUMPALA , B.RATNASUNIL

中国有色金属学报(英文版) doi:10.1016/S1003-6326(17)60092-X

搅拌摩擦加工细化AZ91镁合金,研究钻孔过程中不同切割速度和进料速率下晶粒尺寸和二次相对加工特性的影响.经搅拌摩擦加工得到了过饱和AZ91镁合金,晶粒尺寸由(166.5±8.7)μm细化到(21.7±13.5)μm.相比未加工的AZ91镁合金(HV(108.2±15.6)),经搅拌摩擦加工的合金硬度为HV(88.95±6.1),这归因于二次相的减少.然而,搅拌摩擦加工AZ91合金的平均切割力略微减小.相比未加工的AZ91镁合金,搅拌摩擦加工AZ91合金的钻孔边缘损伤较低.因此,虽然在钻孔过程中晶粒细化可以略微增大切割力,但在AZ91镁合金加工过程中边缘处理较好.

关键词: 镁合金 , 搅拌摩擦加工 , 机械加工 , 晶粒尺寸 , 显微组织

A study of the temperature dependence of g factor for MgO:V2+ crystal

Physica B-Condensed Matter

The temperature dependence of EPR g factor for MgO:V2+ crystal has been studied theoretically by considering both the static contribution due to the thermal expansion of crystal and the vibrational contributions due to the electron-phonon interaction of the acoustic and optical branches. The static contribution is calculated from the high-order perturbation formula of g factor and the thermal expansion coefficients alpha(T) at various temperatures. The vibrational contribution of acoustic phonons is obtained by using a Debye model for the lattice vibrations and that of optical phonons is calculated by use of a single frequency model. The calculated results show that for the g factor at various temperatures, the static contribution is dominant, but for the temperature dependence of g factor, i.e., (dg/dT)(p) or Delta g(T) = g(T) - g(0), the vibrational contributions from the acoustic and optical phonons are comparable with the static contribution due to thermal expansion. It appears that a reasonable theoretical explanation for the temperature dependence of g factor should take all of these contributions into account.

关键词: impurities

Theoretical studies of the g factor of V3+ in III-V semiconductors

Semiconductor Science and Technology

A two spin-orbit coupling parameter model based on a cluster approach is presented in this paper for the calculations of the g factor for V3+ ions in the cation sites of GaP, InP and GaAs crystals. In this model, differing from the conventional one spin-orbit coupling parameter model, both the contributions from the spin-orbit coupling of the central 3d(2) ion and those of ligand ions are included. By using the parameters obtained from the optical spectra of the studied crystals, the calculated g shifts (g - 2.0023) are in good agreement with the observed values. Various contributions to the g shift are discussed.

关键词: electron-paramagnetic-resonance;transition-metal impurities;vanadium;gaas;crystal;epr;spectra;cr2+;gap;inp

Investigation of the zero-field splitting and g factors for V2+ in CsMgCl3

Physica B-Condensed Matter

In this paper, by using only one adjustable parameter V' (the trigonal-field parameter), the zero-held splitting D, the g factors g(parallel to) and Delta g (= g(parallel to) -g(perpendicular to)) for CsMgCl3:V2+ crystal have been calculated from the high-order perturbation formulas based on the two spin-orbit coupling parameter model. The calculated results show good agreement with the observed values. A comparison between the calculated results from various crystal field theories are also made. It is found that the difference between signs D and Delta g for CsMgCl3:V2+ crystal is caused by the contributions from the excited multiplets, particularly those arising from the free ionic term (2)G. (C) 1998 Elsevier Science B.V. All rights reserved.

关键词: crystal and ligand field theory;electron paramagnetic resonance;spin-orbit coupling;V2+ ion;CsMgCl3;crystal;spectra;ions

Studies of the zero-field splitting and g factors for V3+ in CuAlS2 crystal

Journal of Physics and Chemistry of Solids

The zero-field splitting D and g factors g(parallel to),g(perpendicular to) for V3+ ions substituting for Cu+-site and Al3+-site in CuAlS2 ternary semiconductor was calculated by using the high-order perturbation formulas based on the two spin-orbit coupling parameter model where the contributions to EPR parameters from both the spin-orbit coupling of the central 3d(2) ion and that of the ligands are considered. The calculated D, g(parallel to) and g(perpendicular to) for V3+ replacing Cu+-site are in good agreement with the observed values, whereas the calculated D value for V3+ replacing Al3+-site is not. These results show that V3+ substitutes for Cu+-site in CuAlS2 crystal. (C) 1999 Elsevier Science Ltd. All rights reserved.

关键词: semiconductors;crystal fields;defects;electronic paramagnetic;resonance (EPR);superposition model;semiconductors;resonance;spectra

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

g factors and energy spectrum of MgO :;V2+ and their pressure-induced shifts

Communications in Theoretical Physics

The calculations of the whole energy spectrum and the g factors of the ground state and t(2)(3) E-2 excited state for MgO:V2+ at normal pressure as well as their pressure-induced shifts have been carried out on the basis of the theory of pressure-induced shifts and the diagonalization of the complete d(3) energy matrix in a regular octahedral field. The calculated results are in very good agreement with experimental data. It is found that in the range of 1 bar similar to 100 kbar, the g value of the ground state increases monotonously with pressure, but the g value of t(2)(3) E-2 excited state for MgO:V2+ decreases at first, and then increases. For the first time, the physical essentials of the pressure-induced shifts of g values for the ground state and t(2)(3) E-2 excited state have been thoroughly analyzed and revealed by taking into account the wavefunctions, energy spectra and orbital-angular-momentum reduction factors at various pressures.

关键词: high pressure effect;ligand field;optical spectra;line shift;electronic spin resonance;3d transition-metal ions;theoretical calculations;ruby;mgo-cr3+;cr3+;mgo

ZnS:V3+光谱和顺磁g因子的统一解释

谢林华

量子电子学报 doi:10.3969/j.issn.1007-5461.2008.04.002

掺V3+离子的ZnS晶体局部结构与光谱和顺磁共振(EPR)参量有关联.根据Sugano-Tanabe方案建立了d2/8电子强场45×45阶完全能量矩阵,由自旋哈密顿理论推导了EPR参量的计算公式,通过点荷-偶极子模型得到了离子簇局部Td对称结构与晶场参量的关系,基于半自洽场d轨道和完全对角化方法,从局部结构统一解释了ZnS:V3+的光谱和顺磁g因子,计算结果与实验符合.计算结果表明,ZnS:V3+的光谱和EPR谱可以在晶体场理论框架内得到理解.

关键词: 光谱学 , 光学和磁学性质 , 晶体场 , 顺磁g因子 , ZnS

Theoretical studies of the local structures and the g factors for the tetragonal Ti(3+)-V(O) centers in BaTiO(3) bulks and thin films

European Physical Journal-Applied Physics

The local structures and the EPR g factors g(parallel to) and g(perpendicular to) are theoretically studied for the tetragonal Ti(3+)-V(O) centers in BaTiO(3) bulks and thin films using the perturbation formulas of the g factors for a 3d(1) ion in tetragonally elongated octahedra and compressed tetrahedra, respectively, based on the cluster approach. For the Ti(3+)-V(O) center in BaTiO(3) bulks, the impurity Ti(3+) suffers the displacement away from the oxygen vacancy V(O) by about 0.15 angstrom along the C(4) axis due to the electrostatic repulsion of the V(O). Nevertheless, the Ti(3+)-V(O) center in BaTiO(3) thin films may exhibit the tetragonally compressed tetrahedron, characterized by the bond angle 55.88 degrees larger than that (approximate to 54.74 degrees) of an ideal tetrahedron. The quite different g factors (especially g anisotropies Delta g = g(parallel to) - g(perpendicular to)) for the two kinds of samples are discussed, in view of the dissimilar bonding or coordination environments (i.e., incomplete bonding in the thin films may lead to the lower coordination number).

关键词: electron-paramagnetic resonance;atomic screening constants;superposition model;spin-resonance;scf functions;crystals;epr

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