Isotopically driven transitions in LaPrCaMnO system

The effect of oxygen isotope substitution on transport and magnetic properties is studied for (La_1−yPr_y)_0.7Ca_0.3MnO₃ ceramics and thin films. The temperature dependence of electrical resistivity reveals the metal–insulator transition induced by the ¹⁶O→ ¹⁸O substitution at y=0.75 (ceramics) and y=0.5 (films on LaAlO₃). Neutron powder diffraction at y=0.75 demonstrates a striking difference between magnetic structures in the samples with ¹⁶O and ¹⁸O. Measurements of AC magnetic susceptibility allow us to analyze the magnetic phase diagram and its changes related to the isotope substitution.     

High-pressure conductivity studies of blends of poly(p-phenylene)s with oxyethylene side-chains and lithium salts

High-pressure electrical conductivity studies have been carried out with poly(p-phenylene)s with oxyethylene side-chains (PPP(EO)_x/y), which were blended with LiCF₃SO₃. Measurements were performed at pressures up to 280 MPa and at different temperatures. The influences of salt concentration, side-chain length, temperature, and plasticizer content on the relative conductance and activation volume are investigated. The temperature-dependent conductivity of the sample is non-Arrhenius and exhibits Williams–Landel–Ferry (WLF) behavior. The logarithm of relative conductance for PPP(EO)_x/y/LiCF₃SO₃ decreases almost linearly with increasing pressure but increases with salt concentration and side-chain length. As temperature increases, the activation volume becomes smaller but remains positive for PPP(EO)_x/y/LiCF₃SO₃. At higher salt concentrations and longer side-chain lengths, a smaller activation volume for the ion motion is found. These results can be interpreted such that PPP(EO)_x/y/LiCF₃SO₃ behaves like a true polymer electrolyte where ion transport is mediated by segmental motions of the EO side-chains. The addition of tetraethylene glycol dimethyl ether (TEGDME) as a plasticizer increases the activation volume but reduces the conductance.     

The T-contribution to the electrical resistivity at low temperatures in NiAs-type Ni1−xS1−ySey

The y(1−y)-like maxima in Ni_0.98S_1−ySe_y are found beyond y_c in the y-dependences of the coefficient of the T² contribution to the resistivity and of the residual resistivity. Here, the critical concentration of the antiferromagnetic and less-conductive phase is determined to be y_c = 0.095.     

Structural and compositional analysis of InBixAsySb(1−x−y) films grown on GaAs(0 0 1) substrates by liquid phase epitaxy

The growth of epitaxial InBi_xAs_ySb_(1−x−y) layers on highly lattice mis-matched semi-insulating GaAs substrates has been successfully achieved via the traditional liquid phase epitaxy. Orientation and single crystalline nature of the film have been confirmed by X-ray diffraction. Scanning electron micrograph shows abrupt interface at micrometer resolution. Surface composition of Bi(x) and As(y) in the InBi_xAs_ySb_(1−x−y) film was measured using energy dispersive X-ray analysis and found to be 2.5 and 10.5 at.%, respectively, and was further confirmed with X-ray photoelectron spectroscopy. Variation of the composition with depth of the film was studied by removing the layers with low current (20 μA) Ar⁺ etching. It was observed that with successive Ar⁺ etching, In/Sb ratio remained the same, while the As/Sb and Bi/Sb ratios changed slightly with etching time. However after about 5 min etching the As/Sb and Bi/Sb ratios reached constant values. The room temperature band gap of InBi_0.025As_0.105Sb_0.870 was found to be in the range of 0.113–0.120 eV. The measured values of mobility and carrier density at room temperature are 3.1×10⁴ cm² V⁻¹ s⁻¹ and 8.07×10¹⁶ cm⁻³, respectively.     

Preparation, characterization and oxide ion conductivity in U-substituted Bi4V2O11

A Bi₂V_{1 − x − y}U_xBi_yO_{5.5 + 0.5x − y} solid solution derived from Bi₄V₂O₁₁ has been prepared and characterized with x up to 0.125 for y = 0. Partial substitution of U⁶⁺ for V⁵⁺ in Bi₄V₂O₁₁ leads to the stabilization at room temperature of the high-oxide ion conducting γ-phase, in contrast with other M⁶⁺ dopants which stabilize the β-phase. The lower conductivity in U substituted system compared with BICUVOX.10 is attributed to its higher activation energy. Conductivity values and activation energies of the U substituted phases compare well with Bi₂UO₆.     

Entanglement measures of a new type pseudo-pure state in accelerated frames

In this work we analyze the characteristics of quantum entanglement of the Dirac field in noninertial reference frames in the context of a new type pseudo-pure state, which is composed of the Bell states. This will help us to understand the relationship between the relativity and quantum information theory. Some states will be changed from entangled states into separable ones around the critical value F = 1/4, but there is no such a critical value for the variable y related to acceleration a. We find that the negativity N_ABI (ρ^TA_ABI) increases with F but decreases with the variable y, while the variation of the negativity N_BIBII(ρ^TA_ABI) is opposite to that of the negativity N_ABI (ρ^TA_ABI). We also study the von Neumann entropies S(ρ_ABI) and S(ρ_BIBII). We find that the S(ρ_ABI) increases with variable y but S(ρ_BIBII) is independent of it. However, both S(ρ_ABI) and S(ρ_BIBII) first decreases with F and then increases with it. The concurrences C(ρ_ABI) and C(ρ_BIBII) are also discussed. We find that the former decreases with y while the latter increases with y but both of them first increase with F and then decrease with it.     

First principles investigation on Li or Sn codoped hexagonal tungsten bronzes as the near-infrared shielding material

The 52% energy of the solar radiation is contributed by near-infrared radiation (NIR, 780-2500 nm). Therefore, the material design for the energy-saving smart window, which can effectively shield NIR and has acceptable visible transmittance, is vital to save the energy consumed on the temperature control system. It is important to find a non-toxic stable material with excellent NIR-shielding ability and acceptable visible transmittance. The systematic first-principles study on Li_xSn_yWO₃ (x=0, 0.33, 0.66, and y=0, 0.33) exhibits that the chemical stability is a positive correlation with the doping concentration. After doping, the Fermi-energy upshifts into the conduction band, and the material shows metal-like characteristics. Therefore, these structures Li_xSn_yWO₃ (except the structure with x=0.33 and y=0) show pronounced improvement of NIR shielding ability. Our results indicate that when x=0 and y=0.33, the material exhibits the strongest NIR-shielding ability, satisfying chemical stability, wide NIR-shielding range (780-2500 nm), and acceptable visible transmittance. This work provides a good choice for experimental study on NIR shielding material for the energy-saving window.     

不同退火温度的Al_2O_3:C薄膜热释光和光释光性能

α-Al_2O_3:C晶体的热释光和光释光性能优越,但其制备要求高,需高温和高还原气氛.与α-Al_2O_3:C晶体性能接近的α-Al_2O_3:C陶瓷,热释光峰不单一.本文采用两次阳极氧化法在0.5 mol/L的草酸溶液中5℃恒温制备高度均匀有序的多孔Al_2O_3:C薄膜,主要研究不同退火温度对其热释光和光释光特性的影响.结果表明,经不同温度退火后的Al_2O_3:C薄膜均为非晶结构;不同退火温度的Al_2O_3:C薄膜热释光的主发光峰约在310℃左右,符合通用级动力学模型.600℃退火后的Al_2O_3:C薄膜热释光灵敏度最强,其热释光剂量曲线在1-10 Gy范围内具有很好的线性响应,在剂量10-120 Gy范围内出现超线性响应;在相同的辐照剂量下,随着退火温度的升高(≤600℃)光释光的初始发光强度逐渐增强.不同退火温度的Al_2O_3:C薄膜光释光衰减曲线都呈典型的指数衰减且快衰减速率相比α-Al_2O_3:C晶体显著加快.600℃退火后的Al_2O_3:C薄膜光释光灵敏度最强,其光释光剂量响应曲线在1-200 Gy整体上都具有很好的剂量线性关系.与热释光相比,Al_2O_3:C薄膜的光释光具有更宽的线性剂量响应范围.此研究为Al_2O_3:C薄膜作为光释光辐射剂量材料做出了有益的探索.     

Scaling limit of deeply virtual compton scattering

I outline a perturbative QCD approach to the analysis of the deeply virtual Compton scattering process γ^*p → γp′ in the limit of vanishing momentum transfer t = (p′ − p)². The DVCS amplitude in this limit exhibits a scaling behavior described by two-argument distributions F(x,y) which specify the fractions of the initial momentum p and the momentum transfer r ≡ p′ − p carried by the constituents of the nucleon. The kernel R(x,y;ξ,η) governing the evolution of the non-forward distributions F(x,y) has a remarkable property: it produces the GLAPD evolution kernel P(x/ξ) when integrated over y and reduces to the Brodsky-Lepage evolution kernel V(y,η) after the x-integration. This property is used to construct the solution of the one-loop evolution equation for the flavor non-singlet part of the non-forward quark distribution.     

The response of thermally and optically stimulated luminescence from Al2O3:C to high-energy heavy charged particles

The thermoluminescence (TL) and optically stimulated luminescence (OSL) response of Al₂O₃ dosimeters to high-energy heavy charged particles (HCP) has been studied using the heavy ion medical accelarator at Chiba, Japan. The samples were Al₂O₃ single-crystal chips, of the type usually known as TLD-500, and Luxel^TM dosimeters (Al₂O₃:C powder in plastic) from Landauer Inc. The samples were exposed to ⁴He (150 MeV/u), ¹²C (400 MeV/u), ²⁸Si (490 MeV/u) and ⁵⁶Fe (500 MeV/u) ions, with linear energy transfer values covering the range from 2.26 to 189 keV/μm in water and doses from 1 to 100 mGy (to water). A ⁹⁰Sr/⁹⁰Y beta source, calibrated against a ⁶⁰Co secondary standard, was used for calibration purposes. For OSL, we used both continuous-wave OSL measurements (CW-OSL, using green light stimulation at 525 nm) and pulsed OSL measurements (POSL, using 532 nm stimulation from a Nd:YAG Q-switched laser). The efficiencies (η_HCP,γ) of the different HCPs at producing OSL or TL were observed to depend not only upon the linear energy transfer (LET) of the HCP, but also upon the sample type (single crystal chip or Luxel^TM) and the luminescence method used to define the signal—i.e. TL, CW-OSL initial intensity, CW-OSL total area, or POSL. Observed changes in shape of the decay curve lead to potential methods for extracting LET information of unknown radiation fields. A discussion of the results is given, including the potential use of OSL from Al₂O₃ in the areas of space radiation dosimetry and radiation oncology.     

不同粒径α-Al2O3:C晶态粉体热释光和光释光特性

本文探讨了α -Al₂O₃:C晶态粉体的辐照剂量效应, 使用RisøTL/OSL-DA-15 型热释光和光释光仪研究其热释光和光释光特性, 结果发现, 相同粒径的α-Al₂O₃:C晶态粉体具有单一热释光峰, 且随着辐照剂量的增加热释光强度不断增加, 但热释光峰位置保持不变, 符合一级动力学模型; 而在相同的辐照剂量和测试条件下, 随着α -Al₂O₃:C晶态粉体粒径的减小, 其热释光强度先增强后减弱, 热释光峰却逐渐增加至趋于稳定, 表明粒度为40—60 μ的α -Al₂O₃:C晶态粉体具有最佳的热释光效应. 同时α -Al₂O₃:C晶态粉体的光释光特性的研究发现, 其光释光曲线具有典型的指数衰减特征, 粒径对其光释光强度和衰减速率的影响符合浅电子陷阱能级理论.     

Effect of Pr and Ca substitution on superconductivity in Y(1−x−yPrxCay)Ba2Cu3O7−δ

Pr substituted at constant Ca concentration for Y in (Y_1−x−yPr_xCa_y)Ba₂Cu₃O_7−δ superconductors have been prepared under identical conditions and the temperature dependence of the electrical resistivity of these samples are measured. The resistively determined values of T_c decrease linearly with increasing x (0 ≤ x ≤ 0.2) for constant y = 0.10 and 0.15 which provides convincing evidence that the suppression of superconductivity by Pr is mainly due to magnetic pair breaking. The suppression of superconductivity can also be correlated to the observed changes in oxygen content determined by iodometric analysis and to the average Cu-valences. However, it is found that the observed suppression of T_c cannot be compensated by appropriate hole doping with Ca.     

Mg-Al-N三元团簇的密度泛函理论研究

运用杂化密度泛函方法B3LYP在6-311+G^*计算水平上研究Mg_xAl_yN(x,y=1-5)团簇的结构.对Mg_xAl_yN团簇最低能量结构的稳定性和电子特性进行研究.结果表明,Mg_xAl_yN(x+y≤4)团簇的构型主要是平面结构.Mg_xAl_yN团簇的最低能量结构主要是由Al_nN或Mg_x-1Al_y+1N的构型演变而来.Mg_xAl_yN团簇离解成原子或者较小团簇是相对稳定的.和相邻团簇相比,MgAl₃N和Mg₃Al₃N拥有较高的稳定性.随着团簇尺寸的增加,Mg_xAl_yN团簇同时表现出共价键,离子键和金属键的特点.另外,随着团簇尺寸的增加,团簇的垂直电离势和电子亲合能呈现小的震荡,但并没发现整体的变化规律.     

Magnetic properties of one-dimensional CoCu(opba) systems and DFT studies of the building blocks

The synthesis of one-dimensional, molecule-based magnets and the investigation of their structure and physical properties are described. The one-dimensional CoCu(opba) system, where opba [ortho-phenylenebis(oxamato)] bridges the metal ions resulted in antiferromagnetic coupling, and was studied by insertion of electron donating and electron withdrawing groups in the organic ligands’ aromatic rings. In order to verify the influence of these modifications, three compounds of the formula [CoCu(opba-xy)], where x=y=CH₃ (compound 1), x=y=Cl (compound 2), x=H and y=NO₂ (compound 3) are described. The electronic structure of the oxamato bridge group has been studied using calculations at the density functional theory (DFT) level for [Cu(opba-xy)]²⁻ building blocks. Magnetic measurements in polycrystalline samples showed ferrimagnetic behavior for the three compounds. Least-squares fits of the experimental data indicate antiferromagnetic couplings J_CoCu of −35.0, −32.9 and −24.2 cm⁻¹ for 1, 2 and 3, respectively.     

Perovskite-like system (Sr,La)(Fe,Ga)O3−δ: structure and ionic transport under oxidizing conditions

The maximum solid solubility of gallium in the perovskite-type La_1−xSr_xFe_1−yGa_yO_3−δ (x=0.40–0.80; y=0–0.60) was found to vary in the approximate range y=0.25–0.45, decreasing when x increases. Crystal lattice of the perovskite phases, formed in atmospheric air, was studied by X-ray diffraction (XRD) and neutron diffraction and identified as cubic. Doping with Ga results in increasing unit cell volume, while the thermal expansion and total conductivity of (La,Sr)(Fe,Ga)O_3−δ in air decrease with gallium additions. The average thermal expansion coefficients (TECs) are in the range (11.7–16.0)×10⁻⁶ K⁻¹ at 300–800 K and (19.3–26.7)×10⁻⁶ K⁻¹ at 800–1100 K. At oxygen partial pressures close to atmospheric air, the oxygen permeation fluxes through La_1−xSr_xFe_1−yGa_yO_3−δ (x=0.7–0.8; y=0.2–0.4) membranes are determined by the bulk ambipolar conductivity; the limiting effect of the oxygen surface exchange was found negligible. Decreasing strontium and gallium concentrations leads to a greater role of the exchange processes. As for many other perovskite systems, the oxygen ionic conductivity of La_1−xSr_xFe_1−yGa_yO_3−δ increases with strontium content up to x=0.70 and decreases on further doping, probably due to association of oxygen vacancies. Incorporation of moderate amounts of gallium into the B sublattice results in increasing structural disorder, higher ionic conductivity at temperatures below 1170 K, and lower activation energy for the ionic transport.     

TL response of a natural fluorite

A batch of a naturally occurring fluorite (CaF₂) from the Middle Benue Valley region of Nigeria has been studied in some detail for its thermoluminescence (TL) properties. TL glow peaks are observed at 119, 144 and 224°C at a heating rate of 10°C s⁻¹. The TL response is observed to increase with increasing dose, as expected, over the dose range examined. Variations are observed in the decay curves of the various glow peaks with storage at room temperature. While the lower temperature peaks are observed to decay, enhancement of the TL signal is observed for the 224°C glow peak when stored for four weeks. A low-level radioactivity measurement showed no evidence of self-irradiation from naturally occurring radionuclides. UV exposure was suppressed by storage in a black sealed container to exclude sunlight contribution to the observed TL response. A scheme involving the formation of large defect complexes, from smaller ones, during storage, as possible route leading to loss of signal in low temperature glow peaks and a corresponding enhancement at higher temperature, is suggested.     

Magnetic properties of Sm–Co–B-based nanocomposite magnets

The magnetic properties of nanocomposite melt-spun magnets with composition Sm_16−xCo_68+xB₁₆ (x=0–10, 2 at% interval) and Sm₈Co_92−yB_y (y=10–18, 2 at% interval) have been studied systematically. Several ribbons were fabricated with a wheel speed of 50 m/s, followed by annealing in the temperature range of 700–800°C for 2.5–40 min. XRD results and magnetization versus temperature curves showed that almost all of the samples were composed of the tetragonal Sm₂Co₁₄B and rhombohedral SmCo₁₂B₆ phases which are not magnetically hard at room temperature. However, a relatively high coercivity in the range of 3.5–5.5 kOe has been obtained in these samples. The highest coercivity of 5.5 kOe and a very promising β value of −0.28%/°C were obtained in Sm₈Co₇₄B₁₈ ribbons annealed at 750°C for 5 min. The high coercivities are attributed to the small grain size of the 2 : 14 : 1 phase, in which the large surface areas enhance its effective anisotropy, and make it uniaxial type.     

Aliovalent ionic substitution as a probe of conduction mechanism

Silver and sodium have qualitatively different diffraction-determined ionic distributions in the conduction planes of a β-alumina host. That this can imply different conduction mechanisms in the two cases is probed by partially exchanging Cd²⁺ ions into both compounds, and measuring the resulting mixed-ion distributions. The systems Ag_{1.22 − y}Cd_y/2Al₁₁O_17.11 (for y = 0, 0.10, 0.41 and 1.11) and Na_{1.22 − y}Cd_y/2Al₁₁O_17.11 for (y = 0, 0.22, 0.45 and 1.22) were investigated by single-crystal X-ray diffraction. The problematical use of diffraction techniques for highly disordered systems of this type is discussed; it is also shown how some of these difficulties can be reduced through access to additional physical and chemical information. Qualitatively different mechanisms are deduced in the two cases, suggesting that aliovalent substitution can indeed be a useful general tool in studying ionic conduction mechanisms in crystalline systems.     

Spectroscopic study of BixEu1−xVO4 and BiyGd1−yVO4 mixed oxides

The mixed oxides Bi_xEu_1−xVO₄ and Bi_yGd_1−yVO₄ crystallize in a zircon-type structure, for 0 <x < 0.6 and 0 < y < 0.64, and in a fergusonite-type structure, for 0.94 < x < 1 and 0.93 < y < 1. A process of competition between the dominant and the constrained effects of the lone-pair 6s² of Bi³⁺ is discussed. The diffuse reflectance spectroscopic studies of these mixed oxides are presented. The observed broad bands are attributed to charge transfer processes and the sharp peaks in the Bi_xEu_1−xVO₄ spectra are ascribed to intra-configurational 4f – 4ftransitions of the Eu³⁺ ion. The broad absorption shift in BiLnVO₄ (Ln : Eu and Gd) compounds to the longer wavelengths range, when Bi is introduced in the LnVO₄ lattice, is ascribed to charge transfer processes in a Bi-VO₄ center and are interpreted assuming a Jahn-Teller effect in the excited state of Bi³⁺. The concept of an internal pressure of Bi³⁺ ions is also used to explain the broad A-band shifts.     

Effect of cobalt substitution on cationic distribution in LiNi1 − y CoyO2 electrode materials

A crystal chemistry study of LiNi_{1 − y}Co_yO₂ phases, used as positive electrode in lithium batteries, is presented. These materials crystallize in the rhombohedral system (space group: R m) with a layered structure. Rietveld profile refinement of the X-ray data shows that for low substitution amounts ( ≤ 0.20) extra-nickel ions are always present leading to the Li_{1 − z}Ni_{1 + z − t}CotO₂ (t = y(1 + z)) formula (z * > 0), while for y ≥ 0.30, a pure 2D structure is obtained (z = 0). The stabilization of the 2D character of the structure by cobalt substitution in lithium nickelate leads to the improvement of the electrochemical properties.