Solid state reaction synthesis of filled skutterudite compounds (Ce or Y)yFexCo4-xSb12 and the effect of filling atoms Ce or Y on lattice thermal conductivity

The synthesis of filled skutterudite compounds (Ce or Y)yFexCo₄-xSb12, through a solid state reaction using chloride of Ce or Y, high purity powder of Co, Fe, and Sb as starting materials, was investigated. (Ce or Y)yFexCo₄-xSb12 (x = 0 1.0,y = 0 0.15) compounds were obtained at 850 1 123 K. The results of Rietveld analysis demonstrate that (Ce or Y)yFexCo₄-xSb12 synthesized by a solid state reaction possesses a filled skutterudite structure. The filling fraction of Ce or Y obtained by Rietveld analysis agrees well with the composition obtained by chemical analysis. The lattice constant of CeyFexCo₄-xSb12 increases with increasing substitution of Fe at Co sites, and with an increasing Ce filling fraction in the Sb-dodecahedron voids. The lattice thermal conductivity of (Ce or Y)yFexCo₄-xSb12 decreases significantly with an increasing Ce or Y filling fraction in the voids and with substitution of Fe at Co sites.     

Application of microcalorimetry and principal component analysis

Thermogravimetric analysis was used in order to study the reduction in air of submicronic powders of Co_3−x Mn _x O₄ spinels, with 0 ≤ x ≤ 1. For x = 0 (i.e. Co₃O₄), cation reduction occurred in a single step. It involved the Co^III ions at the octahedral sites, which were reduced to Co²⁺ on producing CoO. For 0 < x ≤ 1, the reduction occurred in two stages at increasing temperature with increasing amounts of manganese. The first step corresponded to the reduction of octahedral Co^III ions and the second was attributed to the reduction of octahedral Mn⁴⁺ ions to Mn³⁺. From the individual weight losses and the electrical neutrality of the lattice, the Co^III and Mn⁴⁺ ion concentrations were calculated. The distribution of cobalt and manganese ions present on each crystallographic site of the spinel was determined. In contrast to most previous studies that took into account either Co^III and Mn³⁺ or Co²⁺, Co^III and Mn⁴⁺ only, our thermal analysis study showed that Co²⁺/Co^III and Mn³⁺/Mn⁴⁺ pairs occupy the octahedral sites. These results were used to explain the resistivity measurements carried out on dense ceramics prepared from our powders sintered at low temperature (700–750 °C) in a Spark Plasma Sintering apparatus.     

Thermal analysis study of Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3-x</Subscript>Er<Subscript>x</Subscript>O<Subscript>10+δ</Subscript> glass-ceramic system

Summary We have fabricated glasses in the Bi-2223 HT_c superconductor system with Bi₂Sr₂Ca₂Cu_3-xEr_xO_{10+ δ} nominal composition, where x=0.5 and 1.0, by the glass-ceramic technique. Using an analysis developed for non-isothermal crystallization studies, information on some aspects of crystallization temperature and thermal properties has been obtained. The crystallization studies were made using DTA with several uniform rates. The calculations of crystallization activation energies, E_a, and the Avrami parameters, n, were made based on the non-isothermal kinetic theory of Kissinger and the Ozawa’s equations. The DTA data of the samples showed that the first crystallization temperature, T_x1, increases and the second crystallization temperature, T_x2, decreases by increasing the Er concentration. This suggests that the Er substitution had significant effect on the glassification of the BSCCO material due to change on the surface nucleation and increased ionic activities at high temperature region. The activation energy for crystallization, E_a, of the samples was also showed an increase at high Er concentration case. However, the Avrami parameter, n, decreased from 2.5 to 1.7 for x=0.5 and 1.0 samples, respectively. This suggests that the growth mechanism is diffusion-controlled and three-dimensional parabolic growth takes place near the first crystallization temperature. The oxidization rates and the activation barrier for oxygen out-diffusion process, E, was calculated using the TG data. It was found that the total mass gain in the x=0.5 sample is comparably smaller than that of the x=1.0 sample. This shows that the oxygen absorption of the x=1.0 sample is faster than the x=0.5 sample, leading to increase in the oxidization rate in the x=1.0 material.     

NixCo3-xO4表面修饰对CdSe/TiO2纳米管阵列光电化学氧化水活性的影响

利用氨挥发诱导法在CdSe/TiO2纳米管阵列表面负载一层NixCo3-xO4。采用SEM、XRD、XPS、UV-Vis对样品进行表征,通过线性扫描伏安法测定光阳极的释氧电势来评价其光电水氧化活性。结果表明:表面NixCo3-xO4是尖晶石结构;相对于CdSe/TiO2纳米管阵列光阳极,NixCo3-xO4/CdSe/TiO2光阳极能将光电氧化水的过电势降低430 mV。Ni离子的引入使得NixCo3-xO4表面富含三价阳离子(Ni3+,Co3+),从而促进CdSe/TiO2光阳极光电水氧化的进行。     

Kinetic study of zirconia crystallization from amorphous ZrO2-SiO2 composite precursors processed by sol-gel chemistry

Powder precursor gels with composition xZrO₂·(100–x)SiO₂, with selected values of x=8, 24, 43 and 75 mol%, were processed by sol-gel chemistry. Differential thermal analysis (DTA) was used to study crystallization in (cubic/tetragonal)-ZrO₂ during the heating of the reactive amorphous precursors. Kinetic parameters such as activation energy, Avrami's exponent and frequency factor have been simultaneously calculated from the computed DTA data using a previously reported kinetic model. The crystallization temperature decreases relative to the increase in the amount of ZrO₂, the value of the kinetic parameter of the crystallization being related to the value of x.     

The Neat Ternary Solid K5−xCo1−xSn9 with Endohedral [Co@Sn9]5− Cluster Units: A Precursor for Soluble Intermetalloid [Co2@Sn17]5− Clusters

A new type of Zintl phase is presented that contains endohedrally filled clusters and that allows for the formation of intermetalloid clusters in solution by a one‐step synthesis. The intermetallic compound K_5?xCo_1?xSn₉ was obtained by the reaction of a preformed Co? Sn alloy with potassium and tin at high temperatures. The diamagnetic saltlike ternary phase contains discrete [Co@Sn₉]^5? clusters that are separated by K⁺ ions. The intermetallic compound K_5?xCo_1?xSn₉ readily and incongruently dissolves in ethylenediamine and in the presence of 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane (2.2.2‐crypt), thereby leading to the formation of crystalline [K([2.2.2]crypt)]₅[Co₂Sn₁₇]. The novel polyanion [Co₂Sn₁₇]^5? contains two Co‐filled Sn₉ clusters that share one vertex. Both compounds were characterized by single‐crystal X‐ray structure analysis. The diamagnetism of K_5?xCo_1?xSn₉ and the paramagnetism of [K([2.2.2]crypt)]₅[Co₂Sn₁₇] have been confirmed by superconducting quantum interference device (SQUID) and EPR measurements, respectively. Quantum chemical calculations reveal an endohedral Co^1? atom in an [Sn₉]^4? nido cluster for [Co@Sn₉]^5? and confirm the stability of the paramagnetic [Co₂Sn₁₇]^5? unit.     

LixNi0.5Co0.5O2的态密度计算及电化学性能研究

>为获得综合性能更好的锂离子二次电池正极材料, 分析了Co掺杂对Li_xNiO₂电化学性能的影响. 采用密度泛函DFT理论对Li_xNiO₂和Li_xNi_0.5Co_0.5O₂的平均放电电压和态密度进行了计算. 同时, 用共沉淀法制备了Li_xNiO₂和Li_xNi_0.5Co_0.5O₂锂离子二次电池正极材料, 并对其进行了XRD结构分析和恒流充放电测试. 实验和计算结果表明: 随锂离子嵌入正极(电池放电), 电池的电压逐渐降低, 材料的态密度峰向低能量方向移动; 与Li_xNiO₂相比, Li_xNi_0.5Co_0.5O₂的电压平台相对较高(当0.25≤x≤0.5), 而且在Li^＋嵌/脱时, Li_xNi_0.5Co_0.5O₂的结构变化相对较小; Co离子的掺入, 减小了NiO₆八面体的畸变度, 使材料的电化学稳定性得以提高. 在钴掺杂镍酸锂体系中, NiO₆和CoO₆具有相互的稳定作用.     

Oxygen species and their reactivity in the mechanochemically prepared substituted perovskites La1 ? xSrxCoO3 ? y (x = 0–1)

The oxygen species and their reactivity in the mechanochemically prepared substituted perovskites La_{1 − x} Sr _x CoO_{3 − y} were studied using temperature-programmed reduction (TPR) of the samples with hydrogen. The experimental data were compared with data on the catalytic activity of the series of La_{1 − x} Sr _x CoO_{3 − y} catalysts in the oxidation of CO, as well as with the real structures and surface compositions of the samples, which were studied in detail previously. As the strontium content was increased, the degree of reduction of the samples increased in the course of TPR and the TPR peaks shifted to the region of lower temperatures, except for the last sample containing no lanthanum (x = 1). An increase in the calcination temperature and time resulted in a decrease in TPR peak intensities and in a shift of the peaks to the region of higher temperatures. A reaction scheme was proposed for the reduction. In accordance with this reaction scheme, Co⁴⁺ in substituted cobaltites was reduced to Co⁰ at temperatures lower than 400°C. In the temperature region of 400–500°C, the Co³⁺ → Co²⁺ bulk reduction, as well as the deep reduction processes Co³⁺ → Co⁰ and Co⁴⁺ → Co⁰, occurred; substitution facilitated the above processes. At temperatures higher than 500°C, Co²⁺ → Co⁰ bulk reduction occurred. The observed reduction of the mechanochemically prepared samples depended on their microstructure, which was described previously. It was found that the activity of the samples in the oxidation of CO depends on the amount of the most weakly bound reactive surface oxygen species, which were removed in TPR with hydrogen to 150°C. No correlation between the amount of strongly bound (lattice) oxygen removed upon TPR and the activity of La_{1 − x} Sr _x CoO_{3 − y} samples in the oxidation of CO was found. Original Russian Text ? I.S. Yakovleva, L.A. Isupova, V.A. Rogov, 2009, published in Kinetika i Kataliz, 2009, Vol. 50, No. 2, pp. 290–299.     

Synthesis and photocatalytic properties of low-dimensional cobalt-doped zinc oxide with different crystal shapes

The glycoxide complexes Zn_1–x Co _x (HCOO)(HOCH₂CH₂O)_1/2 and Zn_1−x Co _x (OCH₂CH₂O) (0 ≤ x ≤ 0.3) have been synthesized by heating ethylene glycol solutions of zinc formate Zn(HCOO)₂ · 2H₂O or its mixtures with cobalt formate Co(HCOO)₂ · 2H₂O. The crystals of these complexes have the shape of filaments (needles, bars) and distorted octahedra, respectively. A new method in which these complexes are used as the precursor is suggested for the synthesis of low-dimensional wurtzite-like Zn_1−x Co _x O. The shape of the precursor crystals is fully inherited by Zn_1−x Co _x O resulting from their heat treatment. The Zn_1−x Co _x O solid solutions show high photocatalytic activity in hydroquinone oxidation in aqueous solution under UV or blue light irradiation, and their activity increases as their cobalt content is increased.     

Tb3Pd2, Er3Pd2 and Er6Co5–x: structural variations and bonding in rare‐earth‐richer binary intermetallics

The three binary Tb/Er‐rich transition metal compounds Tb₃Pd₂ (triterbium dipalladium), Er₃Pd₂ (trierbium dipalladium) and Er₆Co_5–x (hexaerbium pentacobalt) crystallize in the space groups Pbam (Pearson symbol oP20), P4/mbm (tP10) and P6₃/m (hP22), respectively. Single crystals of Tb₃Pd₂ and Er₆Co_5–x suitable for X‐ray structure analysis were obtained using rare‐earth halides as a flux. Tb₃Pd₂ adopts its own structure type, which can be described as a superstructural derivative of the U₃Si₂ type, which is the type adopted by Er₃Pd₂. Compound Er₆Co_5–x belongs to the Ce₆Co_2–xSi₃ family. All three compounds feature fused tricapped {TR₆} (R = rare‐earth metal and T = transition metal) trigonal prismatic heterometallic clusters. R₃Pd₂ is reported to crystallize in the U₃Si₂ type; however, our more detailed structure analysis reveals that deviations occur with heavier R elements. Similarly, Er₆Co_5–x was assumed to be stoichiometric Er₄Co₃ = Er₆Co_4.5. Our studies reveal that it has a single defective transition‐metal site leading to the composition Er₆Co_4.72(2). LMTO (linear muffin‐tin orbital)‐based electronic structure calculations suggest the strong domination of heteroatomic bonding in all three structures.     

Glycine-assisted hydrothermal synthesis of nanostructured Co x Ni1−x –Al layered triple hydroxides as electrode materials for high-performance supercapacitors

Nanostructured Co _x Ni_1−x –Al layered triple hydroxides (Co _x Ni_1−x –Al LTHs) have been successfully synthesized by a facile hydrothermal method using glycine as chelating agent. The samples were characterized by X-ray diffraction, thermogravimetry, Fourier transform infrared spectroscopy and scanning electron microscopy. The morphologies of Co _x Ni_1−x –Al LTHs varied with the Co content and its effect on the electrochemical behavior was studied by cyclic voltammetry and galvanostatic charge–discharge techniques. Electrochemical data demonstrated that the Co _x Ni_1−x –Al LTHs with Co/Ni molar ratio of 3:2 owned the best performance and delivered a maximum specific capacitance of 1,375 F g⁻¹ at a current density of 0.5 A g⁻¹ and a good high-rate capability. The capacitance retained 93.3% of the initial value after 1,000 continuous charge–discharge cycles at a current density of 2 A g⁻¹.     

Ferromagnetism study of Co<Subscript>0.2</Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>0.8−<Emphasis Type="Italic">x</Emphasis></Subscript>O films prepared by the sol–gel method

Co_0.2Mg _x Zn_0.8−x O films prepared with different molar ratio of magnesium acetate to zinc acetate were deposited on substrates by the sol–gel technique. X-ray diffraction, photoluminescence (PL) and ferromagnetism measurements were used to characterize the Co_0.2Mg _x Zn_0.8−x O diluted magnetic semiconductors. The acceptor-like defects were determined in the PL band and the intensity of the acceptor-related PL increased with increasing Mg concentration. Therefore, an increase in the number of the acceptor-like defects (zinc vacancies especially) in the Co_0.2Mg _x Zn_0.8−x O film may lead to the enhancement of the magnetic properties. It is worth noting that changes in Mg concentration and the number of the acceptor-like defects are important issues for producing strong ferromagnetism Co_0.2Mg _x Zn_0.8−x O films prepared by the sol–gel method.     

Mn1-x(Li,Ti)xCo2O4尖晶石型复合氧化物的制备、表征与催化性能

用柠檬酸配位燃烧法合成了Mn_1-x(Li,Ti)_xCo₂O₄系列尖晶石型复合氧化物催化剂，使用FTIR和XRD方法对催化剂结构进行表征，通过程序升温氧化反应(TPO)技术对这些催化剂在模拟柴油机尾气条件下进行同时消除NO_x和柴油碳黑反应的活性评价。结果表明，掺杂Li或Ti后的Mn_1-x(Li,Ti)_xCo₂O₄系列催化剂仍然保持了完整的尖晶石型复合氧化物结构，这些催化剂对同时消除柴油机尾气中的碳黑颗粒和NO_x具有良好的催化性能，其中Li或Ti的掺杂量为x=0.05较佳，结合碳黑燃烧与NO_x还原总的催化效果，Mn_0.95Li_0.05Co₂O₄具有最好的催化活性。     

Catalysis of Multi‐walled Carbon Nanotubes Supported PdxCoy Nanoparticles Prepared by a Pyrolysis Method Using Ionic Liquids as the Solvent toward Ethanol Oxidation Reaction

Multi‐walled carbon nanotubes (MWCNTs) decorated with Pd_xCo_y (the nominal atomic ratios of Pd to Co were 3:1, 3:1.5, 3:2, 3:3, respectively) nanoparticles (denoted as Pd_xCo_y/MWCNTs ) were fabricated by a simple pyrolysis process, in which room temperature ionic liquids (RTILs) of butyl‐3‐methylimidazolium hexafluorophosphate (denoted as [BMIM]PF₆) was used as the solvent. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) were all used to characterize the Pd_xCo_y/MWCNTs catalysts, showing that the Pd_xCo_y particles were dispersed on the surface of the MWCNTs with an average particle size of ～25.0 nm. The electro‐catalytic activity of the Pd_xCo_y/MWCNTs catalysts toward ethanol oxidation reaction (EOR) was examined by cyclic voltammetry (CV). It was revealed that the onset potential was ～90 mV lower and the peak current was about four times higher for ethanol oxidation for Pd₃Co_1.5/MWCNTs compared to those of Pd₃Co₁/MWCNTs. The possible catalysis mechanisms of the Pd₃Co_1.5/MWCNTs toward EOR were also discussed.     

Synthesis and electrochemical properties of LiNi0.9-xCo0.1SnxO2 as cathode materials for lithium secondary batteries

LiNi_0.9-x Co_0.1Sn _x O₂ (x = 0.00, 0.02, and 0.03) were synthesized via the rheological phase reaction method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The sample of LiNi_0.9-x Co_0.1Sn _x O₂ (x = 0.02) not only shows good cycle performance but also exhibits an excellent discharge capacity of 188 mAh/g in the first cycle at a current density of 100 mA/g in the voltage range of 3.0–4.3 V. The tin doping results in reducing the resistance and increasing conductivity of LiNi_0.9-x Co_0.1Sn _x O₂. This composite oxide is promising as cathode material for lithium-ion battery.     

Thermal analysis and longtime stability of amorphous Co100−xBx alloys

Crystallization behaviour of amorphous Co_100?xB_x alloys (17 <x ≤ 40) has been investigated by differential thermal analysis (DTA) and dynamic temperature X-ray diffraction (DTXD) methods in the freshly prepared state and at a period of about eight years after preparation. The crystallization temperatures lie in the range 670 K–760 K. An average decrease of about 1.25 K/year over a period of eight years has been observed to take place in the crystallization temperatures of these materials. The value of heat of crystallization (ΔH _cr) and activation energy lie in the range 2.3 kJ/g-at – 5.9 kJ/g-at and 2.1 eV – 2.4 eV, respectively. The phases obtained at crystallization temperatures during DTXD analysis have been discussed.     

Magnetotransport Properties and Kondo Effect Observed in a Ferromagnetic Single‐Crystalline Fe1−xCoxSi Nanowire

We report unconventional magnetotransport properties of an individual Fe_1?xCo_xSi nanowire. We have studied the dependence of the resistivity on the angle between the directions of the magnetization and electrical current below the Curie temperature (T_C). The observed anisotropic magnetoresistance (MR) ratio is negative, thereby indicating that the conduction electrons in a minority spin band of the Fe_1?xCo_xSi nanowire dominantly contribute to the transport. Unlike typical ferromagnets, positive MR is observed in the overall temperature range. MR curves are linear below T_C and show a quadratic form above T_C, which can be explained by the change of density of states that arises as the band structures of the Fe_1?xCo_xSi nanowire shift under a magnetic field. The temperature dependence of the resistivity curve is sufficiently explained by the Kondo effect. The Kondo temperature of the Fe_1?xCo_xSi nanowire is lower than that of the bulk state due to suppression of the Kondo effect. The high single crystallinity of Fe_1?xCo_xSi nanowires allowed us to observe and interpret quite subtle variations in the prominent intrinsic transport properties.     

层状六边形Co1-xS修饰氮掺杂碳纳米管用于锂硫电池的硫载体

通过纳米结构材料的设计和组装来改善锂硫电池的电化学性能。在本工作中,成功合成了六边形Co_1-xS纳米片修饰的氮掺杂碳纳米管（Co_1-xS-CNT）复合材料,并将其用作锂硫电池（LSBs）的硫正极载体。在Co_1-xS-CNT/S中,极性六方Co_1-xS纳米片可以化学吸附多硫化锂,同时CNT可以为电极材料提供高导电网络。基于物理限域和化学吸附的协同作用,Co_1-xS-CNT/S正极表现出优异的电化学循环性能。在0.5C倍率下循环170次,电极仍可保持405.6 mAh·g^-1的放电比容量,同时具有超过99.2%的稳定库仑效率。     

Synthesis and magnetic properties of nanocomposite Ni1?xCoxFe2O4–BaTiO3 fibers by organic gel-thermal decomposition process

Nanocomposites of ferrite and ferroelectric phases are attractive functional ceramic materials. In this work, the nanocomposite Ni_1−x Co _x Fe₂O₄–BaTiO₃(x = 0.2, 0.3, 0.4, 0.5) fibers with fine diameters of 3 ~ 7 μm and high aspect ratios were synthesized by the organic gel-thermal decomposition process from the raw materials of citric acid and metal salts. The structure, thermal decomposition process and morphologies of the gel precursors and the resultant fibers derived from thermal decomposition of the gel precursors were characterized by Fourier transform infrared spectroscopy, thermogravimetric differential thermal analysis, X-ray diffraction and scanning electron microscopy. The magnetic properties of the nanocomposite fibers were measured by vibrating sample magnetometer. The nanocomposite fibers of ferrite Ni_1−x Co _x Fe₂O₄ and perovskite BaTiO₃ are formed at the calcination temperature of 900 °C for 2 h. The average grain sizes of Ni_1−x Co _x Fe₂O₄ and BaTiO₃ in the nanocomposite fibers increase from about 15 nm to approximately 67 nm with the increasing calcination temperatures from 900 to 1,180 °C. The saturation magnetization of the nanocomposite Ni_1−x Co _x Fe₂O₄–BaTiO₃(x = 0.2, 0.3, 0.4, 0.5) fibers increases with the increase of grain sizes of Ni_1−x Co _x Fe₂O₄ and Co content, while the coercivity reaches a maximum value at the single-domain size of about 65 nm of Ni_0.5Co_0.5Fe₂O₄ obtained at the calcination temperature of 1,100 °C.     

A novel coprecipitation method towards the synthesis of Ni<Subscript>x</Subscript>Mn<Subscript>x</Subscript>Co<Subscript>(1–2x)</Subscript>(OH)<Subscript>2</Subscript> for the preparation of lithium metal oxides

A series of mixed metal hydroxide (Ni _x Mn _x Co_(1–2x)(OH)₂) precursors for the preparation of lithiated mixed metal oxides (LiNi _x Mn _x Co_(1–2x)O₂) were prepared using a novel coprecipitation approach based on the thermal decomposition of urea. Three different methods were used to achieve the temperature required to decompose urea and subsequently precipitate the hydroxides. The first two methods consisted of either a hydrothermal or microwave-assisted hydrothermal synthesis at 180 °C and elevated pressures. The final method was an aqueous reflux at 100 °C. A complete series (x = 0.00–0.50) was prepared for each method and fully characterized before and after converting the materials to lithiated metal oxides (LiNi _x Mn _x Co_(1–2x)O₂). We observed the formation of a complex structure after the coprecipitation of the hydroxides. Scanning electron micrographs images demonstrate that the morphology and particle size of the hydroxide particles varied significantly from x = 0.00–0.50 under hydrothermal synthesis conditions. There is also a significant change in particle morphology as the urea decomposition method is varied. The X-ray diffraction profiles of the oxides synthesized from these hydroxide precursors all demonstrated phase pure oxides that provided good electrochemical performance.