Semiconductor-metal transition in novel Cd2Os2O7

Cd₂Os₂O₇ has been prepared for the first time and has the pyrochlore structure with a cubic cell edge of 10.17 Å at room temperature. Electrical, magnetic, and DSC measurements on single crystals of this compound show a sharp transition at 225 K which we interpret to be an electronic, second-order, metal-semiconductor transition. The low-temperature semiconducting phase is probably antiferromagnetic.     

Ferromagnetism of V-doped ZnO nanowires

The geometry structures,electronic structures,and magnetic properties of Zn46V2O48 nanowires are studied by density functional theory(DFT) calculations.We find that the ferromagnetic(FM) coupling is more stable for six configurations of Zn46V2O48 nanowires,and is mediated by neighboring O as evidenced from the strong hybridization of V 3d and O 2p states,exhibiting strong spin polarization.The spin polarization is found to be 100% in the Zn46V2O48 nanowires,which confirms that it is a half-metallic ferromagnet and very suitable for the injection of the spin carriers,which shows that Zn46V2O48 nanowire is one of the ideal materials to realize spin electronic devices.At the same time,the magnetic coupling mechanisms of Zn46V2O48 nanowires are analyzed with V 3d and O 2p orbitals and their magnetic moments mainly come from the contributions of the unpaired electrons of V 3d orbitals.The above results provide a theoretical basis for the preparation of 3d transition metal-doped ZnO nanowire materials.     

Magnetic properties of a Na-doped WS<Subscript>2</Subscript> monolayer in the presence of an isotropic strain

The magnetic properties of Na-doped WS₂ monolayer under strain are investigated by ab initio methods. Without strain, the Na-doped WS2 monolayer is a magnetic nanomaterial and the total magnetic moment is about 1.07μ_B. We applied strain to Na-doped WS₂ monolayer from–10% to 10%. The magnetic properties are modified under different strain; the doped system gets a maximum value of at 2.01μ_B 10% tensile strain and a minimum value of at 0μ_B–10% compressive strain. The coupling between 3p states of S and 5d states of W is responsible for the strong strain effect on the magnetic properties. Our studies predict Na-doped WS₂ monolayer under strain to be candidates for application in spintronics.     

Synthesis and magnetic properties of ordered barium ferrite nanowire arrays in AAO template

BaFe₁₂O₁₉ nanowire arrays having single magnetic domain size (≤460 nm) in anodic aluminum oxide (AAO) templates were prepared by sol-gel and self-propagating high-temperature synthesis techniques. The diameter of the nanowire arrays is approximately 70 nm and the length is about 2-4 μm. The specimens were characterized using X-ray diffraction, vibrating sample magnetometer, field emission scan electron microscope, atomic force microscopy and microwave vector network analyzer. The magnetic properties of BaFe₁₂O₁₉ nanowire arrays embedded in AAO templates were measured by VSM with a field up to 1274 KA/m at room temperature. The results indicate that the nanowire arrays exhibit large saturation magnetization and high coercivity in the range of 6000 Oe and an obvious magnetic anisotropy with the easy magnetizing axis along the length of the nanowire arrays, probably due to the shape anisotropy and magneto-crystalline anisotropy. Finally the microwave absorption properties of the nanowires were discussed.     

Structural, electronic and magnetic properties of Cr-doped Cd12S12 clusters: A density functional investigation

We have carried out first-principles density functional investigation of Cd₁₂S₁₂ cluster doped with one (monodoped) and two (bidoped) Cr-atoms, to explore the manifestation of novel magnetism in this family of stable II-VI semiconducting clusters. Different types of possible configurations of the dopant e.g. substitutional, exohedral, endohedral and substitutional-exohedral have been considered. Both for monodoped and bidoped clusters, substitutional doping corresponds to the ground state. In case of bidoped clusters, the coupling is found to be short-ranged, that depends on the Cr-Cr separation and the local environment. The main competing factors stabilizing ferromagnetic (FM) state in this class of doped nanoclusters are: (a) the FM interaction between two Cr atoms via S atom due to strong p-d hybridization and (b) the short range Cr-Cr direct antiferromagnetic (AFM) interaction. When additional hole is introduced in the system by substituting S with P, in substitutional bidoped clusters, FM state is found to be the ground sate.     

First principles study on electronic structure of β-Ga2O3

We have studied the electronic structure of β-Ga₂O₃ using the first principles full-potential linearized augmented plane wave method. It is found that β-Ga₂O₃ has an indirect band gap with a conduction band minimum (CBM) at Γ point and a valence band maximum on the E line. The anisotropic optical properties are explained by the selection rule of the band-to-band transitions. On the other hand, the shape of the CBM is almost isotropic and, therefore, the observed electronic anisotropy in the n-type semiconducting state should not be attributed to the properties of a perfect lattice. The Burstein-Moss shift is discussed using the effect of several allowed transitions between the levels of the valence band and the CBM.     

Ab initio studies on n-type and p-type Li4Ti5O12

This paper studies the structure and electronic properties of Li4Ti5O12, as anode material for lithium ion batteries, from first principles calculations. The results suggest that there are two kinds of unit cell of Li4Ti5O12: n-type and p-type. The two unit cells have different structures and electronic properties:the n-type with two 16d site Li ions is metallic by electron, while the p-type with three 16d Li ions is metallic by hole. However, the Li4Ti5O12 is an insulator. It is very interesting that one n-type cell and two p-type cells constitute one Li4Ti5O12 supercell which is insulating. The results show that the intercalation potential obtained with a p-type unit cell with one additional electron is quite close to the experimental value of 1.5 V.     

A first-principle prediction on the magnetism and electronic structure of Ti-doped CoO with two O vacancies

The electronic structure and magnetism in Co₁₄Ti₂O₁₄ systems are investigated by using the first-principles calculations. The system of 2 × 2 × 2 Co₁₄Ti₂O₁₆ supercell doped with Ti at 9 and 11 position shows a half-metallic character with a high spin polarization. Based on the above system, we remove two O atoms to form two O vacancies. The two O vacancies near Ti have a huge effect on the electronic structure and magnetic properties of Co₁₄Ti₂O₁₄ system. When O vacancies locate at 1 and 3 positions, the system shows a half-metallic character. For the O vacancies at 6 and 8 positions, the system shows a semiconducting character. The system with O vacancies at 9 and 11 positions is a typical spin gapless semiconductor.     

First principles study of structural,phonon, optical,elastic and electronic properties of Y3Al5O12

Structural, phonon, optical, elastic and electronic properties of Y₃Al₅O₁₂ have been investigated by means of the first principles method with the Cambridge Serial Total Energy Package (CASTEP) code based on the density functional theory. The calculated lattice parameters, valence charge density, bond length and single crystal elastic properties at zero pressure are in good agreement with the available experimental data. The close agreement with the experimental values provides a good confirmation of the reliability of the calculations. Optical, elastic and phonon properties of Y₃Al₅O₁₂ under pressures are performed. The results that are obtained show the changes of optical and elastic properties under the influence of applied pressure, and proving the dynamical stability of YAG are destructed when applied pressure up to 7 GPa. Moreover, polycrystalline elastic moduli are deduced according to the Reuss assumption. Those elastic constants provide important parameters that describe reliability of both physical model and engineering application at the atomistic level. The result of the density of states explains the nature of the electronic band structure.     

B36团簇组装一维纳米线的密度泛函研究

采用密度泛函理论计算方法系统研究了B₃₆团簇组装一维纳米线的几何结构、电子结构及稳定性.发现两种不同构型的B₃₆团簇组装纳米线静态结构能量相同,且均为动力学稳定结构,但二者电子结构明显不同:分别呈现出半金属和小带隙半导体特征.对两类纳米线的H原子吸附显示:半金属纳米线转变为半导体,而半导体纳米线仍保持为半导体,但带隙明显增大.表明H原子吸附对于B₃₆团簇组装纳米线的电子结构具有明显的调控作用.     

Structural,electronic and catalytic performance of single-atom Fe anchored 3Si-doped graphene

By density functional theory (DFT) calculations, it is found that the single-atom Fe anchored three Si modified defective graphene (3Si-graphene-Fe) exhibits the high stability, and this system is semiconducting property and has non-magnetic moment. Besides the most stable configurations, electronic structures and magnetic properties of adsorbed species (O₂, CO, 2CO and CO/O₂) on 3Si-graphene-Fe systems are comparably discussed. The adsorption of O₂ is more stable than that of CO molecule and the coadsorption of 2CO and CO/O₂ has the larger adsorption energy than that of the isolated one. The adsorbed O₂, CO and CO/O₂ can induce the change in magnetic properties of 3Si-graphene-Fe system, and the coadsorbed CO/O₂ on system exhibits the metallic property. Among the reaction mechanisms, the CO oxidation reactions through Eley–Rideal (ER) reactions have lower energy barriers (<0.5?eV) than those of the Langmuir–Hinshelwood (LH) and new termolecular Eley–Rideal (TER) mechanisms, indicating that the ER reaction as starting step is an energetically favourable process. These results provide an important guidance on validating the catalytic activity of single atom on graphene-based materials.     

Electronic and structural properties of Ti9XO20 (X=Ti,C, si,Ge, Sn and pb) clusters: A DFT study

The electronic and structural properties of Ti₉XO₂₀ (X=Ti, C, Si, Ge, Sn and Pb) clusters have been obtained in the density functional theory (DFT) framework. The changes in the bond length, binding energy, frontier orbitals, and electronic potential have been fully analyzed when one titanium atom in the (TiO₂)₁₀ cluster is replaced by elements with four valence electrons. When one titanium atom is substituted by one carbon atom, a charge excess among the guest and the surrounding oxygen atoms is generated, which is approximately 1.5 times that of the pristine case, and this structure has been shown to be the most stable among the studied systems. In addition, the Ti₁₀O₂₀–Cd₂ and Ti₉CO₂₀–Cd₂ clusters exhibit HOMO–LUMO gaps that have decreased by 0.58 and 2.12 eV, respectively, with respect to the bare cases.     

A photoelectrochemical study of the hexagonal ferrite PbFe12O19

Several techniques have been used in order to characterize the photoelectronic properties of a magnetoplumbite single crystal of composition Pb_1.19Fe_11.88O_18.91. Measurements of electrical resistivity and thermoelectric power have shown between 77 and 300 K the compound to have n-type semiconducting properties. The I–V characteristics (in the dark and under illumination), the spectral response and the flat band potential have also been determined.The density of donors derived from Mott-Schottky plots (3.2 × 10¹⁹) is in good agreement with the value of the Fe²⁺ concentration (2.9 × 10¹⁹) obtained by chemical analysis. Electron affinity was found to be equal to 4.5 ± 0.2 eV. The photocurrent corresponding to the photoelectrolysis of water is due to indirect electronic transitions at 1.75, 2.1 and 2.4 eV. Evidence is given suggesting that these transitions correspond to lead-iron and/or iron-iron charge transfers.     

Electronic bandstructures on 5d-transition metal pyrochlore: Cd2Re2O7 and Cd2Os2O7

The electronic bandstructure calculations for Cd₂Re₂O₇ and Cd₂Os₂O₇ are performed by using an FLAPW method based on the local density approximation, where the spin–orbit interactions are taken into account. It is found that the spin–orbit interaction changes significantly Re/Os-5d (t_2g) band dispersion situated near the Fermi level. Cd₂Re₂O₇ is a semi-metal, the Fermi level is located just in the valley, the specific heat coefficient is calculated as 2.7 mJ/K² mol Re and the carrier number is 0.039/cell in each hole and electron. The Re/Os-5d bands hybridize well with the O-p bands so that the Re/Os-5d component significantly appears even in the bottom of the wide O-p bands. Therefore, it is important to consider Re-5d O-p hybridization to investigate the physical properties of these compounds.     

Magnetic and electric properties of transition-metal doped wurtzite CdSe from first-principles calculations

The geometrical structures of Cd_0.75TM_0.25Se (TM = Ti, V, Cr and Mn) are optimized, and then their electric and magnetic properties are investigated by performing first-principles calculations within the generalized gradient approximation for the exchange--correlation function based on density functional theory. Cd_0.75TM_0.25Se (TM = Ti and V) are found to have high spin-polarization near 100% at the Fermi level. Cd_0.75TM_0.25Se (TM = Cr and Mn) are half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely +100%. The supercell magnetic moments of Cd_0.75Cr_0.25Se and Cd_0.75Mn_0.25Se are 4.00 and 5.00~μ_B, which arise mainly from Cr-ions and Mn-ions, respectively. The half-metallicity of Cd_0.75Cr_0.25Se is more stable than that of Cd_0.75Mn_0.25Se. The electronic structures of Cr-ions and Mn-ions are Cr e_g²↑ t_2g²↑ and Mn e_g²↑ t_2g³↑, respectively.     

Mg12O12纳米线掺杂3过渡金属元素的第一性原理计算研究

基于密度泛函第一性原理计算,系统研究了Mg12O12笼状团簇组装一维纳米线及其掺杂3d族元素体系的几何结构与电子结构。结果表明：Mg12O12团簇组装一维纳米线为非磁性半导体,带隙值为3.16 eV;掺杂Sc和V后,体系由半导体转变为金属;掺杂Ti、Cr、Mn、Fe、Co、Ni、Cu后体系仍然保持半导体特性、但带隙值明显减小,而掺杂Zn时带隙值变化不大;掺杂V、Cr、Mn、Fe、Co、Ni、Cu后纳米线具有磁性。     

Advanced electrochemical performances of Li4Ti5O12/Ag prepared by a facile synthesis route

Spinel Li₄Ti₅O₁₂ coated by highly dispersed nanosized Ag particles was synthesized via a facile and effective ultrasonic-assisted method in this paper. X-ray diffraction (XRD) results indicated that Ag was not doped into the lattice of spinel Li₄Ti₅O₁₂. The as-synthesized Li₄Ti₅O₁₂/Ag exhibited enhanced electronic conductivity and excellent electrochemical performances. Its electronic conductivity was increased about four times compared to that of the pristine Li₄Ti₅O₁₂. Even at 10 C rate, the as-synthesized Li₄Ti₅O₁₂/Ag could keep 86.5 % of the reversible capacity at 1 C rate and its reversible capacity was higher than 140 mAhg^?1 whereas those were 75.3 % and 118 mAhg^?1 for the pristine Li₄Ti₅O₁₂.     

Effect of electron correlations on the electronic structure and magnetic properties of the perovskite-like high-pressure phase ErCu3V4O12

The electronic structure and magnetic properties of double perovskite ErCu₃V₄O₁₂ have been investigated in the framework of the projector augmented-wave method. It has been shown that the electron correlations play an important role: the calculations in the one-electron approximation predict that the ground state of ErCu₃V₄O₁₂ is a magnetic metallic state, while with the inclusion of electron-electron correlations, it is a ferrimagnetic semimetallic state. It has been found that the magnetic Cu-Cu and V-V couplings are ferromagnetic and that the Cu-V magnetic coupling is antiferromagnetic.     

Rings, towers, cages of ZnO

Theoretical electronic structure studies on (ZnO)_n (n= 2–18, 21) have been carried out to show that the transition from an elementary ZnO molecule to the bulk wurtzite ZnO proceeds via hollow rings, towers, and cages. Our first principles electronic structure calculations carried out within a gradient corrected density functional framework show that small Zn_nO_n (n=2–7) clusters form single, highly stable rings. Zn₃O₃ and the symmetric cage Zn₁₂O₁₂ are shown to be particularly stable clusters. Among larger clusters, the most stable are oblong cages, Zn₁₅O₁₅, Zn₁₈O₁₈, and Zn₂₁O₂₁, which are reminiscent of nanotubes.     

Low-temperature transport properties of individual SnO2 nanowires

Stannic oxide (SnO₂) nanowires have been prepared by Chemical vapor deposition (CVD). The low-temperature transport properties of a single SnO₂ nanowire have been studied. It is found that the transport of the electrons in the nanowires is dominated by the Efros-Shklovskii variable-range hopping (ES-VRH) process due to the enhanced Coulomb interaction in this semiconducting nanowire. The temperature dependence of the resistance follows the relation lnR∼T^−1/2. On the I-V and dI/dV curves of the nanowire a Coulomb gap-like structure at low temperatures appears.