Synthesis and microstructure of Ca-doped BaTiO3 ceramics prepared by high-energy ball-milling

The calcium-substituted barium titanate ceramics were prepared by solid state reaction technique. High-energy ball-milling was used for processing the powder. The microstructure of Ba_1−xCa_xTiO₃ ceramics was investigated by SEM techniques. The microstructure of Ba_1−xCa_xTiO₃ ceramics shows dense and uniform micrograph in all samples and the grain size is large. In this study the quantitative analysis of the ceramographs is shown and the variation of the different parameters with various doping concentration is discussed. Compositional analysis is ascribed to the occupancy of some Ca²⁺ to the Ti⁴⁺ sites.     

Magnetic properties of magnetite prepared by ball-milling of hematite with iron

Magnetic properties of magnetite powder prepared by ball-milling of stoichiometric mixture of hematite and iron in an inert atmosphere are reported. Hysteresis loops, isothermal remanence acquisition curves and temperature dependence of magnetic susceptibility measurements are used to characterise this material and to examine the effects of heating in air and in an argon atmosphere. Ball-milling of hematite with iron during periods ranging from 30 min up to almost 5 h yields magnetite which exhibits high magnetic hardness, characterised by coercive force three times higher than that typical for single-domain natural magnetites. However, the magnetite produced is unstable upon heating in air, reoxidising almost completely to hematite. Heating in an argon atmosphere causes enhancement of typical magnetic parameters, but decreases the magnetic hardness.     

EPR study of the Ag6S3O4 compound prepared by two methods

The temperature dependence of the EPR spectra of the recently discovered Ag₆S₃O₄ phase in the Ag-O-S system prepared by two methods, the known method of co-precipitation from aqueous solution and a new method depending on the interaction of Ag₂S and Ag₂SO₄ solid reagents, has been investigated. No EPR spectra were observed at room temperature, while at liquid helium temperature a number of EPR spectra have been recorded, which disappeared upon increasing temperature up to liquid nitrogen temperature. The sample obtained by the co-precipitation method revealed an intense, rich EPR spectrum that has been tentatively interpreted assuming the presence of at least two different Ag²⁺ ion complexes, one monomer resulting in an intense anisotropic, rhombic EPR powder pattern with g₁ = 1.93(1), g₂ = 2.025(3), g₃ = 2.094(5), hyperfine constants A₁ = = A₂ = 60(5) · 10^?4 cm^?1,A ₃ = 90(5) · 10^?4 cm^?1 and one dimer EPR pattern presumably involving a pair of Ag²⁺ ions with internuclear separation of 4.3 Å. However, the presence of larger clusters could not be excluded. On the other hand, the sample obtained by a solid state reaction method has given rise to two rather weak EPR lines centered at g_eff = 2.105(3) and g_eff = 4.213(3), respectively.     

电弧炉制备的Sm2Fe17-χCrχ化合物的结构与磁性

通过X射线衍射、磁测量等手段对电弧炉制备的不同热处理条件的Sm2Fe17-χCrχ(χ=1-3)化合物的结构和磁性进行了研究.结果表明1050℃下退火5 d的Sm2Fe17-χCrχ(χ=1-3)化合物具有菱方相的Th2Zn17型结构,同样温度下退火7 d的Sm2Fe17-χCrχ(χ=2.5,3.0)化合物具有单斜晶系的Nd3(Fe,Ti)2型结构.分析表明与重稀土元素的E2Fe17-χCrχ化合物不同,较长的退火时间以及高含量的Cr可以使得Sm-Fe-Cr化合物的3:29相更加稳定.对晶胞体积及晶胞参数的分析结果表明在Sm2Fe17-χCrχ化合物中存在着较强的各向异性的磁体积效应.磁测量研究结果表明在Th2Ni17型结构及Th2Zn17型结构中,Cr对哑铃晶位上的Fe原子的替代无论是对居里温度还是对磁晶各向异性的影响都是不同的,在Th2Ni17型结构中的影响比较大,在Th2Ni17型结构中的影响比较小.     

Structure of nanodiamonds prepared by laser synthesis

A study is reported of nanodiamonds obtained by a new method—pulsed laser ablation of a specially prepared carbon target. In the mechanism employed to produce a diamond phase, this method is similar to that of detonation synthesis of nanodiamonds. The main structural characteristics of the material have been determined and compared with the corresponding characteristics of detonation nanodiamonds.     

On the state of superdense configurations

During gravitational compression of superdense astronomical objects the rest mass of the component particles of the object is a variable quantity and is determined along with the other parameters of the system from the condition of equilibrium. The theory of such systems should begin from the symmetry of the formE ²-p ₁ ² -p ₂ ² -p ₃ ² -m²= 0,p ₅=m, c=?=1. For this reason the dimension of the phase space should be enlarged from six to seven. In this paper the fundamental thermodynamic quantities of an equilibrium system in a seven-dimensional phase space are defined, and several examples of their application are considered for the equation of state of a degenerate Fermi gas in a seven-dimensional phase space. It is shown as a separate question in the statistical theory of multiple creation of particles, that the fluctuations of the thermodynamic quantities in such a system are large ΔA/A ～ 1, and gravitational condensation in an expanding Friedman universe is discussed.     

电磁复合场制备匀质Zn-Bi偏晶合金的物理模拟

本文通过物理模拟的方法研究了强磁场复合交变电流作用对过偏晶合金凝固组织的影响机理,考察了电磁复合场下第二相初生液滴直径的演变规律,以及洛伦兹力作用下已分层少数相被"打碎"进入基体相的过程.结果表明:电磁体积力的增加,有利于液滴初始直径的减小;而交变电流频率的影响存在最佳值,偏离该值对初生液滴直径的抑制效果下降,这与实际试验规律一致;在电磁复合场作用下,已经分层的两液相可以重新实现均匀混合.这些效应有效缓解了偏晶合金凝固前第二相由于各种因素导致的偏聚,模拟结果直观地揭示了电磁复合场制备匀质偏晶合金的主要机理 关键词： 电磁复合场 偏晶合金 物理模拟     

Quantum chromodynamics and the theory of superdense matter

At high enough density and/or temperature ordinary matter undergoes a transition into a plasma-like phase, consisting of quarks and gluons rather than of separate hadrons. Due to asymptotic freedom, the asymptotic properties of such matter can be calculated perturbatively, while in the discussion of phase transitions one should concentrate on nonperturbative effects. Recent progress in this theory is reviewed, as well as its applications to such topics as hadronic structure, neutron stars, high energy collisions of hadrons, etc.     

On the formation of collapsed superdense nuclei in the universe

The possibility of the production of putative superdense nuclei (SDNs) in the universe is studied with the assumption that the SDNs can certainly be formed when nucleons are compressed over some critical density. Possible nuclear astrophysical processes for SDN production taking place in the early big-bang universe, in interstellar space and in ejection from neutron stars are investigated. It is found that the SDNs cannot be produced at all in a hot universe regardless of the properties of SDNs. The situation that would occur in a cold universe is also discussed. A finite amount of SDNs is found to be formed in interstellar space as the product of high-energy reactions between primary cosmic rays and interstellar matter. It also becomes clear that the astration of SDNs thus formed plays no essential role for the enhancement of the number of SDNs. On the other hand, the SDNs originating from neutron stars are estimated to have a cosmic abundance relative to Si as high as 8 × 10^?8??5, which is, apparently, in contradiction with observations. Some implications of this are discussed.     

Structure, electrochromic and optical properties of WO3 film prepared by dip coating-pyrolysis

The tungsten oxide (WO₃) film was grown by dip coating-pyrolysis method with the PEG-400 as the structure-directing agent. Microstructure of the WO₃ film was characterized by TG-DSC, XRD and SEM techniques. It was found that the film annealed at 350 °C for 2 h comprised cubic WO₃ and orthorhombic WO₃. The measurements of the cyclic voltammetry (CV) and UV-vis spectrum suggested that the WO₃ film had a good electrochromic reversibility performance. The film possessed excellent modulation to the visible light and the maximal average transmittance modulation reached 70.06%.     

Improve the field emission uniformity of carbon nanotubes treated by ball-milling process

Carbon nanotubes (CNTs) deposited by chemical vapor deposition (CVD) were treated by ball milling. The morphologies and field emission properties of the treated CNTs depending on milling time were studied. The emission turn-on field is increased, and the field emission current density is reduced, when the milling time increased from 0.5 to 3 h. The as-deposited long CNTs were cut to short CNTs (∼1 h) and micro-particles (>1 h) with increasing of the milling time. It is found that the optimized milling time is 0.5-1 h, the treated CNTs showed excellent field emission properties, such as low turn-on field, high emission current density and uniform luminescence spots distribution.     

Formation of budesonide/α-lactose glass solutions by ball-milling

The possibility to obtain amorphous budesonide stabilised by blending with an excipient characterised by a higher glass transition temperature, namely α-lactose, has been studied. We carried out the mixing of the two compounds at room temperature by ball-milling. The four obtained blends (containing, respectively, 10, 30, 50 and 70%_w of budesonide) are X-ray amorphous and exhibit a single glass transition located between the ones of pure milled crystalline compounds. This revealed that the two amorphous phases are miscible whatever the composition and sufficiently mixed to relax as a whole. Ball-milling thus appears as a powerful tool to form amorphous molecular alloys with enhanced stability properties.     

Relativistic effects in the theory of gravitating fast-rotating superdense configurations

The equations describing fast-rotating gravitating superdense configurations with the account of relativistic corrections in the first-order post-Newtonian approximation are obtained.     

LiC分子基态及其低电子激发态的多参考组态相互作用方法研究

采用包含Davidson修正的多参考组态相互作用(MRCI+Q)方法结合6-311++G(3df,3pd)基组计算了LiC分子基态(X4Σ-)以及五个低电子激发态(a2Π,b2Δ,c2Σ-,d2Σ+,A4Π)的势能曲线.将得到的势能曲线拟合到Murrell-Sorbie解析势能函数形式,确定了对应态的平衡结构Re、谐振频率ωe和离解能De等光谱数据,计算值与仅有的几个其他结果进行了比较.通过求解核运动的薛定谔方程首次报道了LiC分子几个低电子态在J=0下的振动能级、转动惯量和六个离心畸变常数(Dν,Hν,Lν,Mν,Nν和Oν).     

Structure of (Ba0.7Sr0.3)TiO3 films prepared by chemical solution deposition on sapphire substrates

Barium strontium titanate (BST) films on single-crystal sapphire substrates are prepared by chemical solution deposition upon annealing at temperatures T = 700, 850, and 1000°C. The structure of the BST films is investigated using transmission electron microscopy, high-resolution electron microscopy, and x-ray diffraction. It is established that, upon annealing at T = 700 and 850°C, the film crystallizes in the tetragonal phase of the (Ba_0.7Sr_0.3)TiO₃ perovskite without texture and transition layers. The mean grain sizes are 17 and 37 nm, respectively. However, an increase in the annealing temperature to 1000°C brings about a decrease in the mean grain size to 25 nm and the appearance of additional phases due to the interaction at the film-substrate interface.     

Structure and hard magnetic properties of barium hexaferrite with and without La2O3 prepared by ball milling

The barium hexaferrites have been prepared by ball milling of a BaO₂ and Fe₂O₃ mixture followed by thermal heat treatments. The structure and magnetic properties were investigated using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer techniques. The effect of grain refiner was also studied and it was found that the hard magnetic properties were improved significantly. The sintered product of barium hexaferrite powders prepared from ball milling has higher coercive force than that of other barium hexaferrite made from oxide/carbonate.     

Structure of high-Tc superconducting Bi-Sr-Ca-Cu-O films prepared by spray pyrolysis

High-T_c superconducting films of Bi-Sr-Ca-Cu-O have been synthesized by spray pyrolysis of nitrate precursors onto yttria stabilized zirconia (YSZ), followed by rapid annealing at 840°C in air/oxygen. The films are preferentially oriented with c-axis parallel to the plane of the substrate surface. The diffraction patterns of the films correspond to a mixed phase orthorhombic structure, with different c-values of 24.49 Å, 30.78 Å and 37.25 Å. These films exhibit superconductivity at 91 K and zero resistance at 77 K.     

Structure and stability of Fe−Mg amorphous alloys prepared by coevaporation

The structure, stability and magnetic properties at 77K of Fe₆₀Mg₄₀ amorphous thin films prepared by coevaporation are investigated using mainly Mössbauer effect working in scattering geometry and transmission electron microscopy. The temperature range of the amorphous to crystal transition is determined; moreover a superparamagnetic-like behaviour of the films is pointed out at 77K.

     

Structure and electrical properties of InSb thin films prepared by plasmatic sputtering

This paper describes the apparatus for the plasmatic sputtering and preparation of InSb thin films. The structure and the dependence of the resistance of InSb films on the sputtering time at different temperatures are introduced. The dependences of the Hall constant, Hall mobility and electric conductivity of polycrystalline thin films on the film thickness is explained.     

Structure and magnetic properties of colossal magnetoresistance compound Tb0.5Sr0.5CoO3

The structure and the magnetic properties of the doped rare earth cobaltite systems are of recent interest owing to the CMR phenomenon that occur in them. In this paper, we investigate the structure and magnetic properties of Tb_0.5Sr_0.5CoO₃ solid solution, for the first time, using neutron powder diffraction technique. The sample Tb_0.5Sr_0.5CoO₃ is found to crystallize in orthorhombic (Pbnm) symmetry. The unit cell volume and Co—O bond length reduce with temperature. The calculatede _g bandwidth obtained from structural parameters turns out to be 0.989 eV. Low temperature neutron diffraction profiles exhibit a magnetic contribution to the fundamental Bragg peaks indicating a ferromagnetic ordering belowT _c. The results are compared with Co—O—Co bond angles and Co—O bond length of La_0.5Sr_0.5CoO₃, highlighting the ionic size effects on substitution of Tb ion for La in the compound.