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Valleytronic device based on graphene is recently attracting growing interest because of its potential applications such as in quantum information storage and transmission. However, one of the major challenges in designing valleytronic devices is to realize the large valley polarization. Therefore, in the present work, we investigate the effect of the electrostatic barrier on the valley polarization in a graphene modulated by two ferromagnetic metal stripes and one strain, where the large valley polarization can be achieved due to the effect of the electrostatic barrier. With the increase in the height or the width of the electrostatic barrier, the degree of the valley polarization will greatly increase. These interesting finds are very helpful for understanding the valley-dependent transport mechanism of electrons in graphene and designing the valleytronic devices based on graphene under the modulation of the electrostatic barrier.

Valley polarization is one basic concept in valleytronic device applications. However, the coexistence of this scenario in graphene under the joint modulation of a realistic magnetic field and a strain has not been reported. Therefore, in this paper, we use the transfer-matrix method to illustrate the effect of a strain on the valley-dependent transport properties of electrons in a graphene with a realistic magnetic field. We find that the valley polarization strongly depends on the strength and the width of the strained barrier rather than on its position. We also find that the 100% valley polarization can be continuously achieved in a broad Fermi energy region by controlling the strain. This point makes it easier to design the new kinds of the valleytronic devices based on graphene modulated by the realistic magnetic field and the strain.

Boron-based metal-free catalysts for oxidative dehydrogenation of propane (ODHP) have drawn great attention in both academia and industry due to their impressive activity and olefin selectivity. Herein, the SiO2 and B2O3 sequentially coated honeycomb cordierite catalyst is designed by a two-step wash-coat method with different B2O3 loadings (0.1%–10%) and calcination temperatures (600, 700, 800 °C). SiO2 obtained by TEOS hydrolysis acts as a media layer to bridge the cordierite substrate and boron oxide via abundant Si OH groups. The well-developed straight channels of honeycomb cordierite make it possible to carry out the reactor under high gas hourly space velocity (GHSV) and the thin wash-coated B2O3 layer can effectively facilitate the pore diffusion on the catalyst. The prepared B2O3/SiO2@HC monolithic catalyst exhibits good catalytic performance at low boron oxide loading and achieves excellent propylene selectivity (86.0%), olefin selectivity (97.6%, propylene and ethylene) and negligible CO2 (0.1%) at 16.9% propane conversion under high GHSV of 345,600 ml·(g B2O3)−1·h−1, leading to a high propylene space time yield of 15.7 g C3H6·(g B2O3)−1·h−1 by suppressing the overoxidation. The obtained results strongly indicate that the boron-based monolithic catalyst can be properly fabricated to warrant the high activity and high throughput with its high gas/surface ratio and straight channels.

As the potential-wide applications in valleytronic devices, the valleytronics, especially the valley polarization in graphene, has attracted much attentions. Thus, in the present work, we study the effect of the applied bias on the valley polarization in a magnetic-strained graphene, which has been not studied as we know. Concretely, we analyze the dependence of the valley polarization on the magnitude, the position, and the width of the applied bias, and obtain the large valley polarization in such a graphene nanostructure which can be easily controlled by the applied bias. This study can promote the realization of the applied bias-tunable valleytronic devices.

Oxidative dehydrogenation of ethylbenzene to styrene featured with a non-equilibrium-limit is an alternative to the direct dehydrogenation process, but often exhibits low styrene selectivity caused by deep-oxidation over metal oxide catalysts. Herein, we report a nonmetallic BN embedded graphitic carbon catalyst which was synthesized by a one-step co-pyrolysis method using boric acid, urea and ammonium iron citrate as the reactants. The obtained catalyst exhibits a high styrene selectivity of 94%. The existence of abundant carbonyl groups and BO species could correspondingly contribute more reaction sites and extra oxygen adsorption sites. A higher styrene formation rate of 5.8 mmol gcat−1 h−1 is thus achieved for our BN embedded graphitic carbon catalyst, whereas this value is 3.4 mmol gcat−1 h−1 for sole carbon nanotubes and 0.2 mmol gcat−1 h−1 for BN. Such promoted reactivity for oxidative dehydrogenation of ethylbenzene is derived from the synergetic and collaborative effect of the nonmetallic BN and graphitic carbon catalyst.

We investigate the valley-dependent transport properties of electrons in a magnetic-strain graphene under the modulation of the Schottky metal (SM) stripe. The valley polarization can be achieved in such a graphene due to the effect of the strained barrier rather than the SM stripe. However, the SM stripe can play an important effect on the degree of the valley polarization, which can be easily controlled through changing the position and/or width of the SM stripe. Furthermore, the applied voltage on the SM stripe also can easily modulate the valley polarization. This study is very useful for understanding and designing the valleytronic devices.

Direct catalytic propane dehydrogenation (PDH) to obtain propylene is a more economical and environmentally friendly route for propylene production. In particular, alumina-supported Cr2O3 catalysts can have better potential applications if the acidic properties could be tuned. Herein, a series of rod-shaped porous alumina were prepared through a hydrothermal route, followed by calcination. It was found that the acidity of the synthesized alumina was generally lower than that of the commercial alumina and could be adjusted well by varying the calcination temperature. Such alumina materials were used as supports for active Cr2O3, and the obtained catalysts could enhance the resistance to coke formation associated with similar activity in PDH reaction compared to the commercial alumina. The amount of coke deposited on a self-made catalyst (Cr-Al-800) was 3.6%, which was much lower than that deposited on the reference catalyst (15.7%). The lower acidity of the catalyst inhibited the side reactions and coke formation during the PDH process, which was beneficial for its high activity and superior anti-coking properties.

BACKGROUND Salvianolate, a common drug for stabilizing heart disease and Angina Pectoris, is considered to be off-label for preventing venous thromboembolism (VTE) or anticoagulation at present. However, many clinical studies have showed that salvianolate can effectively inhibit the deep-vein thrombosis (DVT) incidence, and prevent VTE of perioperative patients in the real world in China. OBJECTIVE This analysis aimed to evaluate the effectiveness and safety of salvianolate in preventing VTE in perioperative patients. METHODS Databases of PubMed, Cochrane Library, Embase, CNKI, Wanfang and VIP were searched until July 2019. Literature retrieval, data extraction and quality assessment were independently completed by two researchers and checked with each other. Review Manager 5.2 software was applied for meta-analysis. RESULTS A total of 429 studies were retrieved, including 11 randomized controlled trials (RCTs) with a total of 1149 subjects. Compared with low molecular weight heparin (LMWH) group alone, salvianolate combined LMWH group had lower DVT incidence in preventing perioperative thrombosis (2.75% and 14.23%, OR: 0.21, 95% CI:[0.08,0.53]; P = .0009). The incidence of adverse reactions of experimental group was similar to that of control group (1.79% and 2.31%, OR: 0.65, 95% CI:[0.18,2.35]. P = .51). Compared with the control group, D-dimer level (D-D), platelet count (PLT), fibrinogen (FIB), whole blood high shear viscosity (WBHSV), and whole blood low shear viscosity (WBLSV) were all significantly decreased (P

Based on the transfer-matrix method, a systematic investigation of electron transport properties is done in a monolayer graphene modulated by the realistic magnetic field and the Schottky metal stripe. The strong dependence of the electron transmission and the conductance on the incident angle of carriers is clearly seen. The height, position as well as width of the barrier also play an important role on the electron transport properties. These interesting results are very useful for understanding the tunneling mechanism in the monolayer graphene and helpful for designing the graphene-based electrical device modulated by the realistic magnetic field and the electrical barrier.

As the key factor for designing the valleytronic devices is to well understand the valley-dependent transport mechanism in graphene, we investigate, in this work, the effect of two ferromagnetic (FM) metal stripes on the valley polarization in a graphene nanostructure with a strain. The nearly 100% valley polarization is observed at certain energy windows and it can be easily controlled through changing the width and the position of the FM stripe as well as the strength of the magnetic field induced by the FM stripe. Our interesting findings reveal the valley-dependent transport mechanism of electrons and promote the realization of the new types of valleytronic devices modulated by the FM stripe and the strain.

Using the transfer matrix method, we theoretically study the electron transport properties in a graphene-based magnetic nanostructure modulated by a Schottky metal (SM) stripe, which can be experimentally realized by depositing a ferromagnetic metal (FM) stripe and a SM stripe on the top and bottom of the monolayer graphene. From the numerical results, we find that the electron transmission and the conductance strongly depend not only on the incident angle of carriers and the strength of the magnetic field, but also on the applied voltage on the SM stripe and the width of the SM stripe as well as the position of the SM stripe. These results may be very helpful for understanding the electron tunneling in graphene and for designing the graphene-based nanodevices.

We study the valley-dependent electron transport properties in a graphene under the joint modulation of the magnetic field and the strained barrier. In studying, the effect of the magnetic field on the valley-dependent electron conductance and the valley polarization is considered. From the numerical results, we deduce that a large valley polarization nearly 100% can be obtained in such a magnetic-strained graphene, and the polarization is mainly governed by the strength and the position of the right magnetic field. Moreover, the distance between the right magnetic field and the strained barrier plays an important effect on the valley polarization. These interesting-theoretical finds can promote the realization of the new types of the magnetic field-tunable valleytronic devices.

To find environment-friendly and low pest resistance natural mosquitocide, The insecticidal activity of the essential oil extracted from fructification ofIllicium verumagainstAedes albopictusandCulex pipiens quinquefasciatuswere investigated. The compositions of this oil was analyzed by GC-MS. The results are given as follows, The 24-h LC50values ofIllicium verumessential oil for I, II, III, IV-instar larvae and pupa ofAedes albopictus/Culex pipiens quinquefasciatuswere 4.93/2.04, 8.36/2.96, 11.88/8.42, 16.10/13.13 and 42.31/75.12 μg·mL-1, respectively. A total of 18 compounds identified fromIllicium verumoil, the major volatile components were trans-anethole with the peak area percentage of 94.8%, followed by 1-(3-methyl-2-butenoxy)-4- (1-propenyl) benzene (3.2%), estragole (0.4%), linalool (0.3%) and limonene (0.3%). The results indicates thatIllicium verumoil can be developed into a botanical mosquitocide.

We theoretically investigate the magnetoresistance (MR) effect in a monolayer graphene modulated by both magnetic and electrical barriers, which can be experimentally realized by depositing two parallel metallic ferromagnetic tripes under an applied voltage on the top and bottom of a graphene. The tremendous MR can be found due to the significant difference between the transmissions through the parallel and antiparallel magnetization configurations, and the MR ratio strongly depends on the strength of the magnetic field and the height of the electric barrier. Therefore, we can control the MR effect by changing either of the two magnetic fields or the electric barrier to make a MR device based on a graphene.

We investigate the electron transport in a monolayer graphene modulated by the magnetic–electric barriers, which can be experimentally realized by depositing a ferromagnetic metal (FM) stripe and a Schottky metal (SM) stripe on top of the monolayer graphene. It is shown that the electron transmission and the conductance are strongly dependent not only on the incident energy and the incident angle of carriers, but also on the applied voltage and the width of the SM stripe as well as the strength of the magnetic field. These can be very helpful for exploring the tunneling mechanism of magnetically and electrically modulated graphene.

Using the transfer matrix method, we theoretically investigate the electron transport properties in a three-barrier structure based on monolayer graphene. The numerical results show that the transmission probability and the conductance strongly depend on the barrier height, the barrier width and the incident energy as well as the incident angle of carriers. Therefore, by changing the configuration of the structure, the electron transport properties can be adjusted to be suitable for the practical application in various graphene-based electronic devices such as the graphene-based transistor with the high on/off ratio and the direction-dependent wave vector filter.

The repellent activitie of Cinnamomum japonicum oil against Aedes albopictus were investigated. The main volatile chemical components of the oil were qualitatively studied. The main results are given as follows. Cinnamomum japonicum oil providing absolute protection against Ae. albopictus in laboratory and field for 2.33 ± 0.63 h, 3.85 ± 0.21 h at concentration of 1.5 mg/cm2, respectively. A total of 28 compounds were identified. The main components of the essential oil were borneoll (28.30%), 1,8-cCineole (20.98%), (-)-bBornyl acetate (6.65%), linalool (5.94%), (-)-.alpha.-terpinol (5.87%), caryophyllene oxlde (5.11%). The results indicates that Cinnamomum japonicum oil has a great potential to be developed into a ecofriendly mosquito repellent.

The giant magnetoresistance (MR) effect is theoretically studied in a magnetically modulated two-dimensional electron gas. We find that the significant transmission difference for electron tunneling through parallel and antiparallel magnetization configurations results in a considerable MR effect. We also find that the MR ratio strongly depends on the magnetic strength and the distance between the left edges of two ferromagnetic strips as well as the temperature.

The local structures and spin Hamiltonian parameters (g factors g(parallel to), g(perpendicular to) and the hyperfine structure constants) for the trigonal Co(2+) centers in LiNbO(3) and LiTaO(3) are theoretically studied from diagonalization of the 6 x 6 energy matrix within (4)T(1) ground state for a 3d(7) ion under trigonal symmetry. The contributions from the admixtures of various J (=1/2, 3/2, 5/2) states and the ligand orbitals and spin-orbit coupling interactions, which were usually ignored in the previous studies, are taken into account in this work. From the calculations, the impurity Co(2+) is found not to occupy exactly the host Li(+) site but to undergo an off-center displacement 0.06 angstrom (or 0.03 angstrom) away from the oxygen octahedron center in LiNbO(3) (or LiTaO(3)). The theoretical spin Hamiltonian parameters based on the above local structures show good agreement with the experimental data. The various contributions to these parameters are also discussed. (C) 2008 Elsevier B.V. All rights reserved.

The electron paramagnetic resonance (EPR) parameters (g factors g //, g ⊥ and the hyperfine structure constants) for the interstitial Co2+ center in NH4I are theoretically investigated by the diagonalization of the 6×6 energy matrix of the 4T1 ground state for a 3d7 ion under tetragonal symmetry. The contributions from the admixtures of various J (=1/2, 3/2, 5/2) states and the ligand orbital and spin–orbit coupling interactions, which were normally ignored in previous works, are taken into account in the present treatments. The contributions to the EPR parameters are discussed, and the discrepancies between the calculated hyperfine structure constants and the experimental data are also analyzed.

The electron paramagnetic resonance g factors and the local structure for Ni3+ in LaAl0.9Ni0.1O3 (LAN), La0.75Y0.25Al0.99Ni0.01O3 (LYAN) and YAl0.9Ni0.1O3 (YAN) are theoretically studied from the perturbation formulas of the g factors for a 3d7 ion of low spin (S = 1/2) in tetragonally elongated octahedra. In these formulas, the contributions to the g factors from the tetragonal distortion, characterized by the tetragonal field parameters Ds and Dt are taken into account. According to the calculations, the ligand octahedra around Ni3+ are suggested to suffer 2% relative elongation along the [001] (or C4) axis due to the Jahn-Teller effect.

The defect structures for two Rh2+ centers {A} and {O} in LiD are theoretically studied by analyzing their experimental EPR parameters, based on the perturbation formulas of these parameters for a 4d(7) ion with low spin (S = 1/2) in tetragonally compressed octahedra and orthorhombically elongated octahedra. Center {A} call be attributed to the substitutional Rh2+ at the Li+ site, associated with the next nearest neighbouring (nnn) Li+ vacancy V-Li along [0 0 1] (or C-4) axis as the compensator. In this center, the intervening ligand D- in Rh2+ and the V-Li is found to shift towards Rh2+ by an amount Delta Z(A) approximate to 0.01 angstrom due to the electrostatic repulsion of the V-Li. Center {O} is assigned to the elongation delta approximate to 0.072 angstrom of the ligand octahedron along [0 0 1] axis due to the Jahn-Teller effect, associated with one nnn V-Li along [1 0 0] (or X) axis. The intervening ligand may also suffer a displacement Delta X-o approximate to 0. 11 angstrom towards Rh2+. In the calculations of the hyperfine structure constants, the reduction factors H (approximate to 0.49 and 0.93) due to the Rh2+ 4d-5s orbital admixture are obtained for centers {A} and {0}. (C) 2007 Elsevier B.V. All rights reserved.

The local structures and the spin Hamiltonian parameters of the tetragonal Ru3+ centers in AgCl and AgBr are theoretically studied from the perturbation formulas of these parameters for a 4d(5) ion in tetragonally distorted octahedra. In these formulas, the contributions from the spin-orbit coupling coefficient and the s- and p- orbitals of the ligands are taken into account from the cluster approach. Based on the studies, the impurity centers are attributed to the substitutional Ru3+ occupying the Ag' site associated with one and two next nearest neighbouring cation vacancy V-Ag along the [100] (or C-4) axis for AgCl and AgBr, respectively. Due to the electrostatic repulsion of the V-Ag, the halide ligand(s) intervening in the V-Ag and the impurity Ru3+ are found to displace away from the vacancy by an amount Delta Z approximate to 0.156 angstrom (or 0.185 angstrom) along the C-4 axis for AgCl (or AgBr), respectively. The theoretical results based on the above defect models and the displacements Delta Z show good agreement with the experimental data. The contributions to the spin Hamiltonian parameters from the ligand orbitals and spin-orbit coupling coefficient are also discussed. (c) 2007 Elsevier B.V. All rights reserved.

The spin Hamiltonian parameters, g factors and the hyperfine structure constants for Co4+ (3d5) and Ir4+ (5d5) in SrTiO3 are theoretically studied from the formulas of these parameters for an n d5 (n = 3 and 5) ion in a tetragonally distorted octahedron with low spin S = 1/2. According to the theoretical analyses, the impurity–ligand bond lengths R ′‖ parallel to the C4 axis are found to be larger than the host values R‖ based on the phase transition rotation angles ϕ of the [TiO6]8– octahedron by the C4 axis at 4.2 and 77 K, respectively. The elongation of the ligand octahedra in the host may be enhanced in the impurity centers by the Jahn–Teller effect of the n d5 ions. The theoretical results based on the above local structures show good agreement with the experimental data. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

The electron paramagnetic resonance parameters, zero-field splittings (ZFSs) b 2 0 , b 4 0 , b 4 4 , b 6 0 , b 6 4 and the g factors for Gd3+ on the tetragonal Y3+ site in KY3F10 are theoretically studied from the superposition model for the ZFSs and the approximation formula for the g factor containing the admixture of the ground 8S7/2 and the excited 6L7/2 (L=P, D, F, G) states via the spin-orbit coupling interactions, respectively. By analysing the above ZFSs, the local structure information for the impurity Gd3+ is obtained, i.e., the impurity-ligand bonding angles related to the four-fold (C4) axis for the impurity Gd3+ center are found to be about 0.6° larger than those for the host Y3+ site in KY3F10. The calculated ZFSs based on the above angular distortion as well as the g factors are in reasonable agreement with the observed values. The present studies on the ZFSs and the local structure would be helpful to understand the optical and magnetic properties of this material with Gd dopants.

The zero-field splitting D of the 8 S 7/2 ground singlet for the tetragonal Gd 3+ center in La 2-x Sr x CuO 4 is theoretically studied from the superposition model. Meanwhile, the g factor is also quantitatively investigated from the approximation formula including admixture of the ground 8 S 7/2 and the excited 6 L 7/2 ( L=P , D, F, G) states via the spin-orbit coupling interactions. The calculated zero-field splitting and g factor are in reasonable agreement with the experimental data. It is found that the significant zero-field splitting can be ascribed to the average impurity-ligand bonding angles [≈ (θ1 + θ2)/2 ≈ 62°] related to the four-fold axis larger than that (≈ 54.74°) of the cubic case. Nevertheless, the experimental g factor close to 2 may be largely due to the very slight admixture of the ground 8 S 7/2 and the excited 6 L 7/2 states via the spin-orbit coupling interactions.

The EPR g factors g // and g ⊥ for the six-coordinated Cu 2+(1) site in YBa 2 Cu 3 O 6+x are theoretically investigated from the perturbation formulas for a 3 d 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 Cu 2+(1) site, by considering the effective elongation of the oxygen octahedron due to the Jahn-Teller effect of the Cu 2+ 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 Δ g (= g // - g ⊥). 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.

The defect structure and the anisotropic g factors of a tetragonal Ni3+ center in PbTiO3 are theoretically investigated from improved perturbation formulas of the g factors for a 3d7 ion with low spin S = 1/2 in tetragonally elongated octahedra, established in this work. Based on the studies, the distance between the impurity Ni3+ and the center of the oxygen octahedron is found to be about 0.14 Å, which is smaller than that (≈ 0.3 Å) for the host Ti4+ site due to the inward shift (≈ 0.16 Å ) towards the center of the oxygen octahedron. The theoretical g factors based on the above defect structure agree well with the observed values.

The local angular distortions around the impurity Co2+ in CdCl2, CdBr2 and PbI2 are theoretically studied from the perturbation formulas of the electron paramagnetic resonance (EPR) parameters, the g factors g(//) and g(perpendicular to) and the hyperfine structure constants A(//) and A(perpendicular to) for a 3d(7) ion in trigonal symmetry. In these formulas, the contributions from the s-orbitals of the ligands, which were often ignored, are taken into account based on the cluster approach. By analyzing the EPR spectra, we find that the impurity-ligand bonding angles beta related to the C-3 axis in the Co2+ impurity centers are different from the corresponding metal-ligand bonding angles beta(H) in the hosts, characterized by the local angular distortions Delta beta (=beta - beta(H)). The calculated EPR parameters, especially the anisotropies of the g and A factors for the studied systems based on the local angular distortions Delta beta, show reasonable agreement with the observed values.

The axial displacements for Co2+ and Ni3+ in Al2O3 are theoretically investigated starting from the perturbation formulas of the EPR parameters for a 3d7 ion with high spin (S=3/2) and low spin (S=1/2) in trigonal symmetry, respectively. Based upon these studies, the Co2+ is found to shift towards the center of the oxygen octahedron by an amount ZCo (≈ 0.03 Å) along the C3 axis, while the Ni3+ may suffer another axial displacement ZNi (≈ −0.38 Å) away from the center of the octahedron. The calculated EPR parameters based upon the above axial displacements show good agreement with the observed values. The differences in the EPR parameters and the axial displacements for the two 3d7 ions are discussed.

The spin Hamiltonian parameters g‖ and g⊥ and the hyperfine structure constants A‖ and A⊥ of a tetragonal VO2+ center in (NH4)2SbCl5 are investigated, using the perturbation formulas for a 3d1 ion in tetragonally compressed octahedra. In these formulas, the contributions to the spin Hamiltonian parameters from the s- and p-orbitals as well as the spin-orbit coupling coefficient of the Cl− ligand are taken into account, based on the cluster approach. According to these studies, compression of the ligand octahedra results from the strong axial crystal-fields due to the short V4+-O2− bond in the [VOCl4]2− cluster. The obtained spin Hamiltonian parameters agree well with the experimental data and need fewer adjustable parameters than the previous studies. The covalency of the studied system is also discussed.

The local structures of the two rhombic Ni3+ centers (on the substitutional and interstitial sites) in rutile (TiO2) are theoretically studied from the perturbation formulas of the g factors for a 3d(7) ion of low spin (S = 1/2) in rhombically distorted octahedra. In these formulas, the contributions to the g factors from the low symmetrical parts of the crystal-fields as well as the spin-orbit coupling interaction and orbitals of the ligands are taken into account. From the investigations, the ligand octahedron in the substitutional Ni3+ center may suffer a slightly larger axial elongation (characterized by the axial distortion angle Delta alpha(s) approximate to -1.09 degrees) than that (Delta alpha(H)(s) approximate to -0.73 degrees) in the host and the much smaller perpendicular distortion (characterized by the rhombic distortion angle Delta theta(s) approximate to -0.75 degrees) than that (Delta alpha(H)(s) approximate to -9.0 degrees) in the host due to the Jahn-Teller effect. For the interstitial Ni3+ center, the ligand octahedron is found to undergo a smaller compression (characterized by the axial distortion angle Delta alpha(i) approximate to 1.48 degrees) than that (Delta alpha(H)(i) approximate to 8.17 degrees) in the host and a slighter rhombic distortion (Delta theta(i) approximate to 0.1 degrees) than that (Delta theta(H)(i) approximate to 7.0 degrees) in the host due to the Jahn-Teller effect. The calculated g factors based on the above structural parameters show better agreement than those based on the host structural parameters and those in absence of the spin-orbit coupling and the orbitals of the ligands with the experimentally observed values. (c) 2006 Elsevier B.V. All rights reserved.

The spin Hamiltonian (SH) parameters (zero-field splitting D, anisotropic g factors g(parallel to) and g(perpendicular to)) and the local structure of the trigonal Cr(3+) centers I, III and IV in CsMgCl(3) are studied using the perturbation formulae for the SH parameters for a 3d(3) ion in trigonal symmetry based on the cluster approach. In these formulae, not only the contributions from the conventional crystal-field (CF) mechanism, but also those from the charge-transfer (CT) mechanism are taken into account. According to the studies, the metal-ligand bond angle related to the C(3)-axis is found to increase from beta(H)(approximate to 51.71 degrees) in the host to beta(approximate to 54.48 degrees) in the impurity center I (in the absence of local charge compensation). As for center III (or IV), the three Cl(-) ions closest to the compensator V(Mg) (or Li(+)) are expected to displace away from the compensator by an amount Delta X(III) approximate to 0.009 nm (Delta X(IV) approximate to 0.003 nm) due to the electrostatic repulsion. The local structure of the trigonal centers and the contributions from the CT mechanism are discussed.