Electronic structure studies of nanoferrite Cu(x)Co(1-x)Fe2O4 by X-ray absorption spectroscopy

Pure and mixed cobalt copper ferrites are of great interest due to their widespread application in electronics and medicine. We report on the electronic structure of a nanoferrite Cu(x)Co(1-x)Fe2O4 (0.0 < or = x < or = 1.0) system studied by X-ray absorption spectroscopy. These magnetic nanoferrites (average crystallite size approximately 31-43 nm) were synthesized by an auto combustion method and are characterized by high resolution X-ray diffraction and near edge X-ray absorption fine structure measurements at the O K and Co, Cu, and Fe L-edges. The O K-edge spectra suggest that there is a strong hybridization between O 2p and 3d electrons of Co, Cu and Fe cations and Fe L3,2-edge spectra indicate that Fe ions coexist in mixed valence states (Fe3+ and Fe2+) at tetrahedral and octahedral sites of the spinel structure. Copper and cobalt ions are distributed in the divalent state in octahedral sites of the spinel structure. The origin of high saturation magnetization and coercivity in cobalt-copper ferrites are explained in light of these results.     

Blue pigment colors from wall painting churches in danger (Portugal 15th to 18th century): identification, diagnosis, and color evaluation

Samples of blue wall paint layers from selected 15th to 18th century religious mural paintings from southern Portugal (Alentejo) have been analyzed using a multi-analytical methodology involving the combination of in situ visible spectro-colorimetry with microanalytical techniques such as optical and scanning electron microscopy and Raman spectroscopy. In situ analyses and micro-sampling were carried out in nine different churches, many in an advanced state of deterioration. The objectives of this study were: (a) to identify and compare the pigments that were used in the blue paint layers across the Alentejo region and through time by analysis of the elemental and mineralogical composition and pictorial techniques, and (b) to correlate the data between the actual color of the paint layer and the state of conservation of the pigments. For the paintings dated from the 16th century forward, the results show a generalized use of smalt blue. To a lesser extent, natural azurite was used despite the geological richness of the region in copper and pyrite ores. In only one painting was an optical blue made of carbon black and lime found. The pigments, pure or mixed with red and yellow ochres, were coarsely ground and used in different concentrations to create three-dimensional effects. These parameters as well as the presence of iron oxides in underlayer paints influence the colorimetric coordinates in the more transparent smalt blue paint layers. The state of conservation of the pigments plays an important role in the alteration of the paint color. A clear example of this is the fading of the smalt blue in several paintings due to lixiviation processes.     

X射线吸收精细结构谱在材料科学中的应用

简单介绍了X射线吸收精细结构谱的物理基础,数据处理方法,讨论了X射线吸收精细结构谱在元素组成,价态和结构环境方面的分析结果。结果显示,在钠钙硅酸盐平板玻璃中,二价铁离子和三价铁离子同时存在。在Ag-Na离子交换后,二价铁离子被银离子氧化成三价铁离子。当Ti2O3和锐钛矿被分别掺入硼硅酸盐玻璃后,钛离子主要以四价存在,Ti^4＋离子占据五重配位点。在玻璃中同时掺入锐钛矿和还原剂C,诱导三价钛离子生成,三价钛离子占据八面体配位点,使得Ti K边预边峰高度降低。包裹在钠钙硅酸盐玻璃中的银纳米颗粒界面存在张应力,使得银晶格膨胀,银原子存在两种结构环境：Ag-O配位和Ag-Ag配位。孤立银原子的存在,使得最近邻Ag-Ag配位数显著降低。     

Quantitation from Tafel analysis in solid-state voltammetry. Application to the study of cobalt and copper pigments in severely damaged frescoes

A novel method, using Tafel plots, for quantifying electroactive species in solid materials when their voltammetric signals are strongly overlapped is described. This is applied to the analysis of submicrosamples from the highly damaged frescoes painted by Palomino (1707) in the ceiling vault of the Sant Joan del Mercat church in Valencia, Spain. These paintings, which were fired in 1936, contained cobalt smalt plus azurite mixtures, this last being altered to tenorite (CuO). The reported method provides a quantitation of the cobalt smalt/azurite, tenorite/(azurite + smalt) relationships in samples, thus providing direct information on pigment dosage (smalt/azurite ratio) in pristine paintings, extent of alteration, and temperature experienced by the frescoes during the gunfire episode. Distinction between Palomino paintings and other painters was clearly obtained due to the presence of malachite in these last.     

In-situ X-ray absorption study of evolution of oxidation states and structure of cobalt in Co and CoPt bimetallic nanoparticles (4 nm) under reducing (H2) and oxidizing (O2) environments

In-situ near edge X-ray absorption fine structure spectroscopy was performed to monitor the oxidation states of Co and CoPt nanoparticles (NPs) of 4 nm size in the presence of H(2) and O(2) in the pressure range of 1 bar and 36 Torr respectively. Platinum helps the rapid reduction of cobalt oxides in hydrogen at a rather low temperature (38 °C). In addition, reversible changes of the oxidation states of cobalt in the Co and CoPt NPs as a function of cycling oxygen pressure (in the range of millitorr to 36 Torr) are quantified and compared. The role of Pt in the process of Co reducing and oxidizing was explored. Our findings permit the prediction of the cobalt oxidation states as the reaction conditions are altered. The experimental results also suggest the presence of tetrahedral structure of Cobalt oxide that differs from the Co(3)O(4) spinel structure.     

Effects of Co content and annealing temperature on the structure and optical properties of CoxMg1−xAl2O4 nanoparticles

Co_xMg_1−xAl₂O₄ (x = 0–0.8) nanoparticles were synthesized by sol–gel method, and characterized by X-ray powder diffraction and transmission electron microscopy. X-ray photoelectron spectroscopy and ²⁷Al solid-state NMR spectroscopy were performed to study the chemical environments of cations in the nanoparticles as a function of cobalt content and annealing temperature. The results show that the crystallite size of the particles is about 20–40 nm. Besides the tetrahedral and octahedral coordinations, the second octahedrally coordinated Al³⁺ ions are observed in the samples. The inversion parameter (two times the fraction of Al³⁺ ions in tetrahedral sites) decreases with the increase of annealing temperature and cobalt content. The fraction of octahedral Mg²⁺ decreases with the increase of Co concentration. The absorption spectra indicate that Co²⁺ ions are located in the tetrahedral sites as well as in the octahedral sites in the nanoparticles. The intensity of the absorption peak corresponding to octahedral Co²⁺ ions (300–500 nm) decreases with increasing annealing temperature.     

Effect of reducing atmosphere on the magnetism of Zn(1-x)Co(x)O (0≤x≤0.10) nanoparticles

We report the crystal structure and magnetic properties of Zn(1-x)Co(x)O?(0≤x≤0.10) nanoparticles synthesized by heating metal acetates in organic solvent. The nanoparticles were crystallized in the wurtzite ZnO structure after annealing in air and in a forming gas (Ar95%?+?H5%). The x-ray diffraction and x-ray photoemission spectroscopy (XPS) data for different Co content show clear evidence for the Co(2+) ions in tetrahedral symmetry, indicating the substitution of Co(2+) in the ZnO lattice. However, samples with x = 0.08 and higher cobalt content also indicate the presence of Co metal clusters. Only those samples annealed in the reducing atmosphere of the forming gas, that showed the presence of oxygen vacancies, exhibited ferromagnetism at room temperature. The air annealed samples remained non-magnetic down to 77?K. The essential ingredient in achieving room temperature ferromagnetism in these Zn(1-x)Co(x)O nanoparticles was found to be the presence of additional carriers generated by the presence of the oxygen vacancies.     

Coordination and valence state of transition metal ions in alkali-borate glasses

Borate glasses of the 20R₂O·80B₂O₃ type, where R = Li, Na and K, were colored by doping with transition metal ions (Co, Ni, Cr and Mn). The glasses were obtained by melting at the temperature of 1150 °C. For these glasses optical absorption in UV–VIS–NIR range were recorded. Analysis of the spectra allows to be determined the coordination and oxidation states of the doping transition metal ions. Changes of their coordination or oxidation are presented as a function of the optical basicity Λ after Duffy. Cobalt and nickel are present in examined borate glasses as divalent ions (Co²⁺, Ni²⁺) in octahedral coordination mainly, but the tetrahedral coordination state of cobalt is also possible. Chromium and manganese are present in the borate glasses in various oxidation state, though Cr³⁺ and Mn³⁺ ions in the octahedral coordination are probably dominant. A decrease of the electronegativity of the modifiers (Li → Na → K) and an increase of the glass matrix basicity cause a shift of the oxidation/reduction equilibrium towards higher valences of the transition metals (Cr⁶⁺, Mn³⁺).     

Influence of reducing-oxidizing conditions on the optical properties of Co(2+)-doped magnesium aluminosilicate glass ceramics and their use as an effective saturable absorber Q switch

Nonlinear optical properties of Co(2+)-doped magnesium aluminosilicate glass ceramics prepared under normal and reducing conditions are studied in the range of the 4A2 --> 4T1(4F) transition of tetrahedral Co2+ ions. The results of passive Q switching of a 1.54-microm Er3+:glass laser with saturable absorbers made of Co(2+)-doped glass ceramics prepared at different conditions are presented. Q-switched pulses of 60 ns in duration and of 4.6 mJ in energy, corresponding to approximately 20% of the Q-switching conversion efficiency, are achieved.     

Structural,optical and magnetic properties of cobalt-doped CdSe nanoparticles

Pure and Co-doped CdSe nanoparticles have been synthesized by hydrothermal technique. The synthesized nanoparticles have been characterized using X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV–Visible), photoluminescence spectroscopy (PL), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and superconducting quantum interference device (SQUID), at room temperature. From XRD analysis, pure and cobalt-doped CdSe nanoparticles have been found to be polycrystalline in nature and possess zinc blende phase having cubic structure. In addition to this, some peaks related to secondary phase or impurities such as cobalt diselenide (CoSe₂) have also been observed. The calculated average crystallite size of the nanoparticles lies in the range, 3–21 nm, which is consistent with the results obtained from TEM analysis. The decrease in average crystallite size and blue shift in the band gap has been observed with Co-doping into the host CdSe nanoparticles. The magnetic analysis shows the ferromagnetic behaviour up to 10% of Co-doping concentration. The increase of Co content beyond 10% doping concentration leads to antiferromagnetic interactions between the Co ions, which suppress the ferromagnetism.     

直流磁控溅射技术制备TiNxOy薄膜

利用直流磁控溅射技术在玻璃衬底上制备了TiNxOy薄膜样品。发现薄膜的颜色、晶体结构、光学性质等都强烈依赖于反应气体的流量。利用光电子能谱（XPS）、X射线衍射（XRD）、UV—Vis分光光度计、扫描电子显微镜（SEM）等测试手段对样品进行表征。结果表明：随着O2流量的逐步增加,薄膜逐渐呈现非晶态,晶粒逐渐变小。薄膜结构从TiN到TiNxOy再向TiO2过渡。透射光谱显示从TiN的不透明逐渐增加到透明度为80％,且吸收阈发生蓝移。     

Bimetallic iron and cobalt incorporated MFI/MCM-41 composite and its catalytic properties

The MFI/MCM-41 composite material with bimetallic Fe and Co incorporation was prepared using templating method via a two-step hydrothermal crystallization procedure. The obtained products were characterized by a series of techniques including powder X-ray diffraction, N₂ sorption, transmission electron microscopy, scanning electron microscope, H₂ temperature programmed reduction, thermal analyses, and X-ray absorption fine structure spectroscopy of the Fe and Co K-edge. The catalytic properties of the products were investigated by residual oil hydrocracking reactions. Characterization results showed that the FeCo-MFI/MCM-41 composite simultaneously possessed two kinds of stable meso- and micro-porous structures. Iron and cobalt ions were incorporated into the silicon framework, which was confirmed by H₂ temperature programmed reduction and X-ray absorption fine structure spectroscopy. This composite presented excellent activities in hydrocracking of residual oil, which was superior to the pure materials of silicate-1/MCM-41.     

纳米钴蓝共沉淀法制备技术

以硝酸钴、硝酸铝为原料,NaOH或尿素为沉淀剂,采用共沉淀法制备纳米钴蓝。考察了Co/Al摩尔比、沉淀剂种类和煅烧温度等因素对纳米钻蓝呈色性能影响,采用包括可见光分度计等多种方法表征了纳米钴蓝的结构及形貌特征及纳米钴蓝色度值。研究结果表明:(1)煅烧温度为1000℃时,当Co/Al摩尔比从1∶3升至1∶1,钴蓝颜色从蓝色依次向蓝绿色、暗绿色转变,同时,以NaOH为沉淀剂制备的钴蓝其亮度比以尿素为沉淀剂制备的钴蓝高;(2)以NaOH为沉淀剂,Co/Al摩尔比为1∶3时,当煅烧温度为900℃,钴蓝呈蓝绿色,当煅烧温度为1000-1100℃,钴蓝呈蓝色;(3)钴蓝不同制备工艺会改变钴d电子层状态,导致钴蓝呈现不同颜色,最终优化工艺制备的纳米钴蓝粒径为45-65nm,呈尖晶石型晶体结构,色度值为CIE(35.86,-12.63,-34.83)。     

Influence of Co-doping on the structural, optical and magnetic properties of ZnO nanoparticles synthesized using auto-combustion method

In the present work, we have interested to understand the influence of cobalt doping on the various properties of ZnO nanoparticles, a series of samples were successfully synthesized using sol–gel auto-combustion method. The effects of Co doping on the structural and optical properties of ZnO:Co nanoparticles were investigated using X-ray diffraction (XRD), scanning electron microscopy, fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy and vibrating sample magnetometer (VSM). With the sensitivity of the XRD instrument, the structural analyses on the undoped and Co-doped ZnO samples reveal the formation of polycrystalline hexagonal-wurtzite structure without any secondary phase. FTIR spectra confirm the formation of wurtzite structure of ZnO in the samples. The optical absorption spectra showed a red shift in the near band edge which indicates that Co²⁺ successfully incorporated into the Zn²⁺ lattice sites. The room temperature PL measurements show a strong UV emission centered at 392 nm (3.16 eV), ascribed to the near-band-edge emissions of ZnO and defect related emissions at 411 nm (violet luminescence), 449 nm (blue luminescence) and 627 nm (orange-red luminescence), respectively. Magnetic study using VSM reveals that all the samples are found to exhibit room temperature ferromagnetism.     

Structural,morphological and optical properties of undoped and Co-doped ZnO thin films prepared by sol–gel process

Undoped and Co-doped ZnO thin films with different amounts of Co have been deposited onto glass substrates by sol–gel spin coating method. Zinc acetate dihydrate, cobalt acetate tetrahydrate, isopropanol and monoethanolamine (MEA) were used as a precursor, doping source, solvent and stabilizer, respectively. The molar ratio of MEA to metal ions was maintained at 1.0 and a concentration of metal ions is 0.6 mol L^?1. The Co dopant level was defined by the Co/(Co + Zn) ratio it varied from 0 to 7 % mol. The structure, morphology and optical properties of the thin films thus obtained were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis), photoluminescence (PL) and Raman. The XRD results showed that all films crystallized under hexagonal wurtzite structure and presented a preferential orientation along the c-axis with the maximum crystallite size was found is 23.5 nm for undoped film. The results of SEM indicate that the undoped ZnO thin film has smooth and uniform surface with small ZnO grains, and the doped ZnO films shows irregular fiber-like stripes and wrinkle network structure. The average transmittance of all films is about 72–97 % in the visible range and the band gap energy decreased from 3.28 to 3.02 eV with increase of Co concentration. DRX, EDX and optical transmission confirm the substitution of Co²⁺ for Zn²⁺ at the tetrahedral sites of ZnO. In addition to the vibrational modes from ZnO, the Raman spectra show prominent mode representative of Zn_yCo_3?yO₄ secondary phase at larger values of Co concentration. PL of the films showed a UV and defect related visible emissions like violet, blue and green, and indicated that cobalt doping resulted in red shifting of UV emission and the reduction in the UV and visible emissions intensity.     

Metal Organic Chemical Vapour Deposited Thin Films of Cobalt Oxide Prepared via Cobalt Acetylacetonate

The single solid source precursor, cobalt (Ⅱ) acetylacetonate was prepared and characterized by infrared spec-troscopy. Thin films of cobalt oxide were deposited on soda lime glass substrates through the pyrolysis (metal organic chemical vapour deposition (MOCVD)) of single solid source precursor, cobalt acetylaceto-nate, Co[C5H7O2]2 at a temperature of 420℃. The compositional characterization carried out by rutherford backscattering spectroscopy and X-ray diffraction (XRD), showed that the films have a stoichiometry of Co2O3 and an average thickness of 227±0.2 nm. A direct energy gap of 2.15±0.01 eV was calculated by the data obtained by optical absorption spectroscopy. The morphology of the films obtained by scanning electron mi-croscopy, showed that the grains were continuous and uniformly distributed at various magnifications, while the average grain size was less than 1 micron for the deposited thin films of cobalt oxide.     

电化学聚合漆酚钴配合物的研究

将电化学聚合得到的聚漆酚(EPU)与氯化钴异丙醇溶液反应生成聚漆酚钴配合物,采用XPS,FT-IR,DMTA,TG-DTA,AES和EPM等手段对其表征,确定该配合物结构即每个钴离子与EPU分子中二个链节单元的羟基发生配位。配合物的钴含量达8.13％,其电阻为1.74E 11Ω(EPU为7.9E 9Ω)。结果表明钴离子与EPU存在配位作用并形成交链,导致其玻璃化转变温度和耐热性能的提高。     

Doping effects of Co(2+) ions on ZnO nanorods and their photocatalytic properties

A series of Zn(1-x)Co(x)O nanorods with dopant content ranging from x = 0.00 to 0.10 was prepared by a wet chemical method. All Zn(1-x)Co(x)O samples were investigated by x-ray diffraction, transmission electron microscopy, energy-dispersion x-ray line mapping analysis, and UV-visible absorption spectroscopy. It was found that Co(2+) ions were homogeneously substituted for Zn(2+) ions in ZnO nanorods. Rhodamine B degradation was used as a probe reaction to evaluate the effect of Co(2+) doping on ZnO nanorods and photocatalytic performance under UV light and visible light irradiation. Co(2+) ions acted as the trapping or recombination centers for electrons and holes, leading to a reduction in photodegradation efficiency under UV light illumination. Alternatively, Co(2+) ions enhanced the optical absorption and produced the photoinduced carriers under visible illumination in terms of two charge transfer transitions involving Co(2+) ions. Consequently, Co(2+) ions substituted in the lattice of ZnO nanorods significantly improved the visible light photocatalytic activity.     

单相Bi0.95Eu0.05Fe0.95Co0.05O3纳米颗粒的结构及其铁磁特性

采用溶胶-凝胶法制备了单相Bi0.95 Eu0.05Fe0.95 Co0.05 O3纳米粉末。用X射线衍射仪(XRD)和扫描电子显微镜(SEM)测量分析了其结构和形貌,结果表明样品仍为钙钛矿菱方结构。样品Fe2p的X射线吸收谱(XAS)表明样品中Fe的价态处于Fe2+和Fe3+的混合态。利用振动样品磁强计(VSM)测量样品的磁性特征,结果表明样品具有完整闭合的磁滞回线,表现出室温的铁磁性,相比BiFeO3样品磁性得到明显增强。     

The optical properties of sputtered Co3O4 films

Films of cobalt oxide were prepared by r.f. reactive sputtering of a cobalt target in Ar-O₂ mixtures, and their optical properties were determined by absorption spectroscopy and scanning ellipsometry. The films were further characterized by electron microscopy and X-ray diffraction. The films were found to consist of Co₃O₄ when the oxygen flow rate exceeded a critical value, in agreement with previous studies. The optical properties of this oxide are due to intense ligand field absorption by Co²⁺ and Co³⁺ ions in a spinel structure. The optical properties of cobalt films oxidized near 500 °C were very similar to those of the sputtered films. Reactive co-sputtering of nickel and cobalt blackened the films for low Ni:Co ratios as a result of charge transfer absorption. Smooth films of Co₃O₄ did not function well as selective thermal absorbers of solar radiation.