Effect of post-annealing on the band gap of sol–gel prepared nano-crystalline Mg x Zn1−x O (0.0 ≤ x ≤ 0.3) thin films

Polycrystalline Mg _x Zn_1?x O (MZO) thin films on glass substrates were prepared by sol–gel method. All the films retained the hexagonal wurtzite structure of ZnO. The band gap values determined from transmission spectra were found to be smaller than the values obtained from Vegard’s law for the as-deposited MZO films. For the films with x = 0.1, 0.2 and 0.3, the band gap blue-shifted initially and then red-shifted with increase in the annealing temperature. The reason for this anomalous shift in the band gap is attributed to the proper substitution of Mg atoms into the Zn lattice sites after a certain critical annealing temperature.     

Influence of Ca2+ substitution on thermal,structural, and conductivity behavior of Bi1−xCaxFeO3−y (0.40 ≤ x ≤ 0.55)

Bi_1?xCa_xFeO_3?y (0.40 ≤ x ≤ 0.55) perovskite oxides have been synthesized by solid-state reaction method to study their properties as a cathode material for intermediate temperature solid oxide fuel cells. The as prepared samples were characterized by X-ray diffraction, differential thermal analyzer/thermogravimetry, dilatometer, and impedance spectroscopy to study their structural, thermal, and electrical properties. The Rietveld refinement results confirmed that all the samples exhibit tetragonal structure with P4mm space group. In addition to this, sample x = 0.55 exhibits Ca₂Fe₂O₅ as a secondary phase. It has been observed that lattice parameters decrease with increase in calcium content. The thermal expansion coefficient and ionic conductivity increases with increase in calcium content up to x = 0.50. The highest ionic conductivity is observed for Bi_0.5Ca_0.5FeO_3?y i.e. 1.71 × 10^?2 S cm^?1.     

Sol–gel synthesis, crystal structure, electronic properties and magnetic studies of B2+xAsxCo4−3xO7 (0.0 ≤ x ≤ 0.75) composites

Synthesis of B_2+xAs_xCo_4?3xO₇ (S1–S4: x = 0.0, 0.25, 0.50 and 0.75) composite oxides were performed by sol–gel method. The powder X-ray diffraction pattern and Reitveld refinement results revels that the samples are formed monoclinic phase with Z = 2 and space group P₂₁/m. Average crystallite size of the samples determined by Scherrer’s relation are found to be ~28–50 nm. The observed and calculated density values are determined and compared. Thermogram shows no phase transition in the range of 50–1,000 °C. The scanning electron micrographs show the morphology of the samples which are observed, the crystallites are rod like shape. The purity and the quantitative analysis were examined by the energy dispersive X-ray. The B–O and Co–O bonds of different sites show marginal variation in the samples, the circular valence charge density contour map of the Co and O in S1–S4 show partial covalent nature of Co–O. Based on the plane-wave density functional theory calculations on crystal structure for band structure and density of states of sample S1–S4 using CASTEP programme package show all the samples are conductor with no band gap. The magnetic moment plot in the range ±10 kG indicates the weak ferromagnetic behavior of the samples. The electron paramagnetic resonance line shapes of all four (S1–S4) samples are isotropic, Diffuse reflectance spectra of sample S1–S4 at room temperature show the band around 273 nm is ligand to metal (O^2? → Co²⁺) charge transfer transition and d–d transition around 570 nm, respectively.     

Phase stability study of the pseudobinary system Gd2O2CO3–Nd2O2CO3 (420 °C ≤ T ≤ 850 °C, P = 1 atm. CO2)

Hexagonal as well as tetragonal rare earth oxycarbonates can act as hosts for optically active ions; hence, the knowledge of the structural modifications occurring when foreign hosts are inserted into the parent compound is of fundamental importance for the design of new phosphors. In this article, a phase stability study of the pseudobinary system Gd₂O₂CO₃–Nd₂O₂CO₃ at P = 1 atm. CO₂ between 420 and 850 °C is presented, to study the amplitude of the existence fields of the different structures typical of rare earth oxycarbonates. The samples were prepared by thermal decomposition of the corresponding oxalates in CO₂ atmosphere. According to composition and temperature, all the three structural forms reported for oxycarbonates (hexagonal, tetragonal, and monoclinic) have been observed. Above a certain temperature, that depends on composition and increases with Nd amount, all the samples decompose into the corresponding Gd–Nd-mixed oxides and crystallize into one of the three possible structural forms typical of rare earth sesquioxides. Structural refinements performed on the hexagonal oxycarbonates demonstrate that the insertion of Nd³⁺ in Gd₂O₂CO₃ results in a linear increase of the lattice parameters (Vegard’s law) and in a reorganization of the distances between and in the CO ₃ ^2? groups and the (Nd/Gd₂O₂)²⁺ layers.     

K?se

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K?segift

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伏安法同时测定维生素K1和K3

维生素 K_1(VK_1)和维生素K_3(VK_3)是使血液凝聚的必要成分,常用光化学法,现代极谱法等测定。用伏安法同时测定VK_1和VK_3迄今未见报导。我们发现在0.0mol/L Na_2SO_4底液中,当pH=4.0～4.3时,VK_1在悬汞电极上发生较强的吸附并还原,而当底液的pH为17.0～1.85时,VK_3在汞电极上还原。它们的导数峰高分别在1.O×10~(-9)～     

Z'(K?)

近年来以Z型机制为转移的光催化体系成微光电化学分解水领域的研究热点.相比较传统的异质结, Z型异质结能够保留具有高氧化能力与高还原能力的位点,从而提高光电化学效率.其中,证明电荷的Z型迁移机制成为研究人员努力的方向,比较有效的证明方法包括自由基捕获、XPS分析和检测还原位点等.对于Z型异质结,界面电场处电荷的迁移行为是至关重要的,但目前常用的证明手段对界面电场处电荷的迁移行为研究还比较少.因此,本文精心设计了CdS/Ti-Fe2O3异质结光阳极来探索光电化学分解水中的电荷转移行为.采用开尔文探针测试、表面光电压谱测试和瞬态光电压谱测试等光物理测试手段监测CdS/Ti-Fe2O3Z型异质结光阳极界面电场中光生电荷的迁移行为.其中,开尔文探针和表面光电压测量表明, CdS/Ti-Fe2O3界面驱动力有利于激发电子快速迁移至Cd S;由于Z型异质结是一个双光子的过程,因此在瞬态光电压的过程中采取了双光束策略,即用不同波长的光分别从两个半导体侧进行照光,以充分发挥内层Cd S的电子传输层的作用.结果表明,在双光束照射下界面电场增强,使得更多Ti-Fe2O3电子与Cd S空穴结合,使得更多Ti-Fe2O3电子与CdS空穴结合,更多的空穴迁移到Ti-Fe2O3的表面去参与反应,充分证明了CdS/Ti-Fe2O3光阳极的Z型迁移机制.基于界面电场有效的电荷迁移与分离的分析,对Z型异质结光阳极进行了光电化学的测试,与单纯Ti-Fe2O3光阳极相比, CdS/Ti-Fe2O3光阳极表现出优异的光电化学性能.其中, 25CdS/Ti-Fe2O3光阳极的光电流密度在1.23V (相对于标准氢电极)达到1.94 mA/cm2,比单纯Ti-Fe2O3光电流高出两倍.阻抗测试结果表明, CdS/Ti-Fe2O3光阳极能够减小电荷传输阻力,从而加快电荷分离效率,这也间接证明了Z型光阳极的成功构筑,因此,本文提供了一个有效且新颖的手段来证明光电化学分解水中光催化系统的Z型电荷转移机制.     

Kβ/Kα intensity ratios following radioactive decay and photoionization

K/K intensity ratios for Cr, Mn, Fe, Cs and Ba have been measured following radioactive decay and photon excitation. A Ge(Li) detector coupled to an ND66B analyzer was used in the measurements. The K/K intensity ratio is affected by the mode of excitation. This effect has a significant influence on K/K intensity ratios of 3d shell elements (Cr, Mn, Fe). However, the effect was found smaller for Cs and Ba.     

荧光法测定维生素K3

维生素K3（Vitamin K3,VK3）是一种油溶性化舍物,不发荧光。L-半胱氨酸（L-cysteine,L-Cys）可将VK3还原为有荧光的甲萘酚,据此建立了一种测定药物制剂中VK3含量的新的荧光分光光度法。甲萘酚的激发波长和发射波长分别为389nm和520nm,荧光强度与VK3的浓度在3.2×10^-7－1.6×10^-5mol／L范围内呈良好的线性关系,相关系数为0.9994,检出限为1.2×10^-9mol／L,平均回收率为98.2％。方法用于VK3注射液的测定,结果令人满意。     

Dependence of the Kβ/Kα intensity ratio on the oxidation state

The K/K X-ray intensity ratios were measured for pure Cr, Mn, Co and Cu belonging to the 3 d shell as well as in their compounds, to look for the influence of the chemical environment on the fluorescence yield ratios. The vacancies in the K shell created by 59.5 keV -rays from an²⁴¹Am source and the X-rays were measured using a Ge(Li) detector. A steady increase of the K/K intensity ratio was observed with increasing oxidation. The present results agree with previously published experimental data.     

HPLC法测定杜仲中维生素K1

为检测杜仲中维生素K1含量,采用了特异性强、分离效果好的高效液相色谱(HPLC)法,将样品经丙酮、石油醚提取,用失活磷酸盐处理过的氧化铝进行柱色谱净化处理,用极性不同的洗脱液将维生素K1从样品中分离出来,收集V(石油醚) V(乙醚)=97 3洗脱组分,浓缩定容,用C18色谱柱对维生素K1进行定性定量分析,流动相为V(甲醇) V(正己烷)=75 25,紫外检测波长为248 nm。结果表明,在流量为1.5 mL/min的条件下,维生素K1的保留时间为(2.18±0.1)min,r为0.999 3,回收率87.67%~95.12%,杜仲中的维生素K1含量为12.404 3μg/g。     

Den Gesamtwassergehalt des K?rpers

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4000°K 的高溫

用 HCN/F_2/O_2混合物燃烧可达4000°K 的高温。这是放243千卡的放热反应(H_2/F_2燃烧放:128千卡)。在高压下燃烧的温度还要增高:在10大气压下     

维生素K1合成的改进

维生素K1分子侧链上有一双键，因而存在几何异构体．天然维生素K1是2，3一反式构型，合成品为顺式和反式异构体的混合物，而顺式异构体几乎没有生理活性．故此，八十年代以后，各国药典均对维生素K；顺式异构体规定了限量，中国药典（1995版）规定顺式异构体的含量不得超过ZI．0％［’］．目前国内流行的制备方法是以甲素配为起始原料，须经还原、乙酸化、水解、缩合、再水解和氧化五步反应制得［’］，步骤长、收率低、对环境污染大．而用异植物酶合成引人侧链时，制备的维生素K；顺式异构体含量较高，达不到药典要求．为满足新版药典的…