The doping effects of BiFe_1-xCo_xO₃（x=0.0-0.8） in layered perovskite Bi₄Ti₃O₁₂ ceramics

Bi5Fe1-xCoxTi3O15(x = 0.0, 0.2, 0.4, 0.5, 0.6, and 0.8) multiferroic ceramics are synthesized in two steps using the solid state reaction technique. X-ray diffraction patterns show that the samples have four-layer Aurivillius phases. At room temperature (RT), the samples each present a remarkable coexistence of ferromagnetism (FM) and ferroelectricity (FE). The remnant polarization (2P r ) reaches its greatest value of 14 μC/cm 2 at x = 0.6. Remnant magnetization (2M r ) first increases and then decreases, and the greatest 2M r is 7.8 menu/g when x = 0.5. The magnetic properties for x = 0.4 are similar to those for x = 0.6, indicating that the magnetic properties originate mainly from the coupling between Fe 3+ and Co 3+ ions, rather than from their own magnetic moments.     

Preparation and the physical properties of antiperovskite-type compounds Cd_1-xIn_x NNi₃（0 ≤x≤ 0.2） and Cd_1-yCu_yNNi₃（0≤y≤0.2）

Two series of Cd1-xInx NNi3(0 ≤x≤ 0.2) and Cd1-yCuyNNi3(0≤y≤0.2) samples were prepared from CdO, In2O3 , CuO, and nickel powders under NH3 atmosphere at 773K. The structural and physical properties were investigated by means of X-ray powder diffraction temperature-dependent resistivity and magnetic measurements. X-ray powder diffraction results showed that the Cd 1 x In x NNi 3 and Cd 1 y Cuy NNi 3 compounds have a typical antiperovskite structure, and the CdNNi3, Cd0.9 In 0.1 NNi3 , and Cd0.9Cu0.1NNi3 compounds show metallic temperature-dependent resistivity and exhibit a Fermi liquid behavior at low temperature. In contrast to the paramagnetism previously reported, the CdNNi 3 sample exhibits very soft and weak ferromagnetism, and no superconductivity was found in the Cd 1 x In x NNi 3 and Cd 1 y Cu y NNi 3 samples down to 2 K. Each sample exhibited very soft and weak ferromagnetism, and the temperature dependence of the magnetization of the Cd 1-xInx NNi 3 and Cd1-y Cu y NNi 3 samples can be well fitted to the combination of a Bloch term and a Curie–Weiss term.     

Intense 2.7 µm emission and structural origin in Er³⁺-doped bismuthate (Bi₂O₃-GeO₂-Ga₂O₃-Na₂O) glass

The 2.7 μm emission properties in Er³⁺-doped bismuthate (Bi₂O₃-GeO₂-Ga₂O₃-Na₂O) glass were investigated in the present Letter. An intense 2.7 μm emission in Er³⁺-doped bismuthate glass was observed. It is found that Er³⁺-doped bismuthate glass possesses high spontaneous transition probability A (65.26 s^-1) and large 2.7 μm emission cross section σ_em (9.53×10^-21?cm²) corresponding to the stimulated emission of Er³⁺:⁴I_11/2→⁴I_13/2 transition. The emission characteristic and energy transfer process upon excitation of a conventional 980 nm laser diode in bismuthate glass were analyzed. Additionally, the structure of bismuthate glass was analyzed by the Raman spectrum. The advantageous spectroscopic characteristics of Er³⁺ single-doped bismuthate glass together with the prominent thermal property indicate that bismuthate glass might become an attractive host for developing solid-state lasers around 2.7 μm.     

The crystal structures and physical properties of the solid solution compound Ba₅Y_8-xMn₄O_21-1.5x（x = 0,1）

New oxometallides with the formula Ba5Y8 xMn4O21 1.5x(x = 0,1) are prepared through an atmospherecontrolled solid-state reaction.Two single-phase samples with Ba/Y/Mn atomic ratios 5/8/4(Y8) and 5/7/4(Y7) are obtained.The crystal structures and the physical properties of the compounds are investigated by X-ray powder diffraction,magnetization,conductivity,and dielectricity measurements.The Ba5Y8 xMn4O21 1.5x compound is demonstrated to be a Y-deficient solid solution.The solid solution compound Ba5Y8 xMn4O21 1.5x crystallizes into tetragonal symmetry with the space group I4/m.Detailed structure analysis by Rietveld refinement of the X-ray powder diffraction data reveals that the Y vacancies occur preferentially at the Y(2) site.Thermal magnetization measurements indicate the presence of antiferromagnetic interaction between Mn ions in the compounds,and temperature-dependent resistivity measurements show that insulator-semiconductor transitions occur around 175 K and 170 K for the Y8 and Y7 samples,respectively.Strong frequency dependences of the dielectric constant are observed above ～175 K for the two compounds.     

Structural analysis and crystal-field calculations of Nd³⁺ in Gd_x Lu_1-x TaO₄（x = 0.85） polycrytalline

The crystal structural parameters of Nd 3+-doped rare earth orthotantalate Gd x Lu 1 x TaO 4(x = 0.85) are determined by applying the Rietveld refinement to its X-ray diffraction,and its emission and excitation spectra at 77 K are analysed.The relativistic model of ab initio self-consistent DV-Xα method,which is applied to the cluster NdO 8 in Gd x Lu 1 x TaO 4,and the effective Hamiltonian model are used to investigate its spin-orbit and crystal-field parameters.The free-ions and crystal-field parameters are fitted to the experimental energy levels at 77 K with a root-mean-square deviation of 14.92 cm 1.According to the crystal-field calculations,96 levels of Nd 3+ are assigned.Finally,the fitting results of free-ions and crystal-field parameters are compared with those already reported for Nd 3+:YAlO 3.The results indicate that the free-ion parameters are similar to those of the Nd3+ in Gdx Lu1-x TaO4 and YAlO 3 hosts,and the crystal-field interaction of Nd3+ in Gdx Lu1-x TaO4 is stronger than that in YAlO 3.     

Step instability of the In_0.2Ga_0.8As （001） surface during annealing

Anisotropic evolution of the step edges on the compressive-strained In0.2Ga0.8 As/GaAs(001) surface has been investigated by scanning tunneling microscopy (STM). The experiments suggest that step edges are indeed sinuous and protrude somewhere a little way along the [110] direction, which is different from the classical waviness predicted by the theoretical model. We consider that the monatomic step edges undergo a morphological instability induced by the anisotropic diffusion of adatoms on the terrace during annealing, and we improve a kinetic model of step edge based on the classical Burton–Cabrera–Frank (BCF) model in order to determine the normal velocity of step enlargement. The results show that the normal velocity is proportional to the arc length of the peninsula, which is consistent with the first result of our kinetic model. Additionally, a significant phenomenon is an excess elongation along the [110] direction at the top of the peninsula with a higher aspect ratio, which is attributed to the restriction of diffusion lengths.     

High stability of the goldalloy fullerenes:A density functional theory investigation of M₁₂@Au₂₀（M=Na,Al,Ag,Sc,Y,La,Lu,and Au） clusters

Discovering highly stable metal fullerenes such as the celebrated C 60 is interesting in cluster science as they have potential applications as building blocks in new nanostructures.We here investigated the structural and electronic properties of the fullerenes M 12 @Au 20(M=Na,Al,Ag,Sc,Y,La,Lu,and Au),using a first-principles investigation with the density functional theory.It is found that these compound clusters possess a similar cage structure to the icosahedral Au 32 fullerene.La 12 @Au 20 is found to be particularly stable among these clusters.The binding energy of La 12 @Au 20 is 3.43 eV per atom,1.05 eV larger than that in Au 32.The highest occupied molecular orbital-lowest unoccupied molecular orbital(HOMO-LUMO) gap of La 12 @Au 20 is only 0.31 eV,suggesting that it should be relatively chemically reactive.     

Does the eigenratio λ₂/λ_N represent the synchronizability of a complex network?

In the study of complex networks,it is commonly believed that the eigenratio λ2/λ N of the Laplacian matrix of a network represents the network synchronizability,especially for symmetric networks.This paper gives two counterexamples to show that this is not true for the case where the network has a disconnected synchronized region.Consequently,a simple answer is presented to the question of when the eigenratio λ2/λ N does represent the network synchronizability.     

Predictions of pressure-induced structural transition,mechanical and thermodynamic properties of α-and β-Si₃N₄ ceramics:ab initio and quasi-harmonic Debye modeling

The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-Si3N4.The ground-state parameters accord quite well with the experimental data.Our calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 K.The α→β phase transformation would not occur in a pressure range of 0-40 GPa and a temperature range of 0-300 K.Actually,the α→β transition occurs at 1600 K and 7.98 GPa.For α-and β-Si3N4,the c axes are slightly more incompressible than the a axes.We conclude that β-Si3N4 is a hard material and ductile in nature.On the other hand,β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0-10 GPa.Besides,the thermodynamic properties such as entropy,heat capacity,and Debye temperature of α-and β-Si3N4 are determined at various temperatures and pressures.Significant features in these properties are observed at high temperature.The calculated results are in good agreement with available experimental data and previous theoretical values.Many fundamental solid-state properties are reported at high pressure and high temperature.Therefore,our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs.     

The analytical potential energy function of flue gas SO₂（X¹A₁）

The equilibrium structure of flue gas SO 2 is optimized using the density functional theory (DFT)/ B3P86 method and CC-PV5Z basis. The result shows that it has a bent (C2V ,X1A1) ground state structure with an angle of 119.1184 . The vibronic frequencies and the force constants are also calculated. Based on the principles of atomic and molecular reaction statics (AMRS), the possible electronic states and reasonable dissociation limits for the ground state of SO2 molecule are determined. The potential functions of SO and O2 are fitted by the modified Murrell–Sorbie+c6 (M-S+c6) potential function and the fitted parameters, the force constants and the spectroscopic constants are obtained, which are all close to the experimental values. The analytic potential energy function of the SO2 (X1A1) molecule is derived using the many-body expansion theory. The contour lines are constructed, which show the static properties of SO2 (X1A1), such as the equilibrium structure, the lowest energies, the most possible reaction channel, etc.     

A k·p analytical model for valence band of biaxial strained Ge on（001） Si_1-xGe_x

In this paper,the dispersion relationship is derived by using the k·p method with the help of the perturbation theory,and we obtain the analytical expression in connection with the deformation potential.The calculation of the valence band of the biaxial strained Ge/(001)Si1-xGex is then performed.The results show that the first valence band edge moves up as Ge fraction x decreases,while the second valence band edge moves down.The band structures in the strained Ge/(001)Si 0.4 Ge 0.6 exhibit significant changes with x decreasing in the relaxed Ge along the [0,0,k] and the [k,0,0] directions.Furthermore,we employ a pseudo-potential total energy package(CASTEP) approach to calculate the band structure with the Ge fraction ranging from x = 0.6 to 1.Our analytical results of the splitting energy accord with the CASTEP-extracted results.The quantitative results obtained in this work can provide some theoretical references to the understanding of the strained Ge materials and the conduction channel design related to stress and orientation in the strained Ge pMOSFET.     

A density functional theory study on the adsorption of CO and O₂ on Cu-terminated Cu₂O（111） surface

The adsorptions of CO and O2 molecules individually on the stoichiometric Cu-terminated Cu2O(111) surface are investigated by first-principles calculations on the basis of the density functional theory.The calculated results indicate that the CO molecule preferably coordinates to the Cu2 site through its C atom with an adsorption energy of -1.69 eV,whereas the O2 molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu2 site and the other O atom coordinating to the Cu1 site,and has an adsorption energy of -1.97 eV.From the analysis of density of states,it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate.The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption,and overlaps substantially with bands of the adsorbed CO molecule.There is a broadening of the 2π orbital of the O2 molecule because of its overlapping with the Cu 3d orbital,indicating that strong 3d-2π interactions are involved in the chemisorption of the O2 molecule on the surface.     

Constraint on the warped space from B→X_sγ

We analyze the theoretical prediction on the branching ratio of B→X_sγ to order Λ_EW²/Λ_KK² in extension of the standard model with a warped extra dimension and the custodial symmetry SU(3)_c×SU(2)_L×SU(2)_R×U(1)_X×P_LR, where Λ_KK denotes the energy scale of low-lying Kaluze-Klein excitations and Λ_EW denotes the electroweak energy scale. Contributions from the in nite series of Kaluze-Klein excitations are summed over through the residue theorem. The numerical result indicates that the present experimental data constrain the parameter space of the concerned model strongly.     

Constraint on the warped space from B→X_sγ

We analyze the theoretical prediction on the branching ratio of B→X_sγ to order Λ_EW²/Λ_KK² in extension of the standard model with a warped extra dimension and the custodial symmetry SU(3)_c×SU(2)_L×SU(2)_R×U(1)_X×P_LR, where Λ_KK denotes the energy scale of low-lying Kaluze-Klein excitations and Λ_EW denotes the electroweak energy scale. Contributions from the in nite series of Kaluze-Klein excitations are summed over through the residue theorem. The numerical result indicates that the present experimental data constrain the parameter space of the concerned model strongly.     

First-principles study of mechanical stability and thermal properties of MNNi₃ （M=Zn,Mg,Al） under pressure

The mechanical stability,elastic,and thermodynamic properties of the anti-perovskite superconductors MNNi 3(M=Zn,Mg,Al) are investigated by means of the first-principles calculations.The calculated structural parameters and elastic properties of MNNi 3 are in good agreement with the experimental and the other theoretical results.From the elastic constants under high pressure,we predict that ZnNNi 3,MgNNi 3,and AlNNi 3 are not stable at the pressures above 61.2 GPa,113.3 GPa,and 122.4 GPa,respectively.By employing the Debye model,the thermodynamic properties,such as the heat capacity and the thermal expansion coefficient,under pressures and at finite temperatures are also obtained successfully.     

Generation of a squeezed state at 1.55 μm with periodically poled LiNbO₃

We report on the generation of a squeezing vacuum at 1.55 μm using an optical parametric amplifier based on periodically poled LiNbO 3.Using three specifically designed narrow linewidth mode cleaners as the spatial mode and noise filter of the laser at 1.55 μm and 775 nm,the squeezed vacuum of up to 3.0 dB below the shot noise level at 1.55 μm is experimentally obtained.This system is compatible with standard telecommunication optical fibers,and will be useful for continuous variable long-distance quantum communication and distributed quantum computing.     

Laser locking to the ¹⁹⁹Hg ¹S₀ - ³P₀ clock transition with 5.4 × 10^-15/✓τ fractional frequency instability

With Hg199 atoms confined in an optical lattice trap in the Lamb-Dicke regime, we obtain a spectral line at 265.6 nm for which the FWHM is ?15??Hz. Here we lock an ultrastable laser to this ultranarrow S₀1?P₀3 clock transition and achieve a fractional frequency instability of 5.4×10^?15/? for ??400??s. The highly stable laser light used for the atom probing is derived from a 1062.6 nm fiber laser locked to an ultrastable optical cavity that exhibits a mean drift rate of ?6.0×10^?17??s^?1 (?16.9??mHz?s^?1 at 282 THz) over a six month period. A comparison between two such lasers locked to independent optical cavities shows a flicker noise limited fractional frequency instability of 4×10^?16 per cavity.     

Growth and photoluminescence properties of inclined ZnO and ZnCoO thin films on SrTiO₃（110） substrates

ZnO thin film growth prefers different orientations on the etched and unetched SrTiO 3(STO)(110) substrates.Inclined ZnO and cobalt-doped ZnO(ZnCoO) thin films are grown on unetched STO(110) substrates using oxygen plasma assisted molecular beam epitaxy,with the c-axis 42 inclined from the normal STO(110) surface.The growth geometries are ZnCoO[100]//STO[110] and ZnCoO[111]//STO[001].The low temperature photoluminescence spectra of the inclined ZnO and ZnCoO films are dominated by D 0 X emissions associated with A 0 X emissions,and the characteristic emissions for the 2 E(2G)→ 4A2(4F) transition of Co 2+ dopants and the relevant phonon-participated emissions are observed in the ZnCoO film,indicating the incorporation of Co 2+ ions at the lattice positions of the Zn 2+ ions.The c-axis inclined ZnCoO film shows ferromagnetic properties at room temperature     

Hcp-icosahedron structural transformation induced by the change in Ag concentration during the freezing of （CoAg）₅₆₁ clusters

The synergy effect of alloy elements in bimetallic clusters can be used to tune the chemical and physical properties. Research on the influences of alloy concentration and distribution on the frozen structure of bimetallic clusters plays a key role in exploring new structural materials. In this paper, we study the influence of Ag concentration on the frozen structure of the (AgCo) 561 cluster by using molecular dynamics simulation with a general embedded atom method. The results indicate that the structure and chemical ordering of the (AgCo) 561 cluster are strongly related to Ag concentration. Hcp-icosahedron structural transformation in the frozen (CoAg) 561 cluster can be induced by changing Ag concentration. The chemical ordering also transforms to Janus-like Co–Ag from core-shell Co–Ag.     

Electronic excitation energies in TiO<Subscript>2</Subscript> in the fluorite phase

The ab initio pseudopotential method within the generalized gradient approximation (GGA) and quasiparticle approximation has been used to investigate the electronic properties of titanium dioxide in the rutile, anatase, and fluorite structures, respectively. Here we present the GW approximation for the electronic self-energy, which allows to calculate excited-state properties, especially electronic band structures. For this calculation, good agreement with the experimental results for the minimum band gaps in rutile and anatase phase is obtained. In the fluorite phase we predict that titanium dioxide will be an indirect (Γ to X) wide band-gap semiconductor (2.367 or 2.369 eV) and the properties remain to be confirmed by experiment.