原位制备钛酸锶钡/铌酸锶钡复相陶瓷的研究

0引言驰豫型铁电陶瓷是近年来广泛研究和迅速发展的一种新型功能陶瓷[1]。通过把具有不同相变温度的驰豫型铁电体层层叠加,可以获得具有稳定的介电常数鄄温度关系的复合材料[2]。钛酸锶钡Ba1-xSrxTiO3和铌酸锶钡SrxBa1-xNb2O6都是重要的驰豫型铁电体,并且其居里温度均随Ba/Sr比     

Dopant position of Co atom in Zn1−xCoxO nanoparticles studied by extended X-ray absorption fine structure

Zn_1?xCo_xO nanoparticles were prepared by sol–gel method. The microstructure and dopant position were studied by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS). The XRD patterns did not show any signal of impurity in the Zn_1?xCo_xO nanoparticles with Co concentration from x = 0.01 to 0.08. Neither did the HRTEM image for the highest concentration sample with x = 0.08. The nanoparticles have also been investigated by the EXAFS measurements at Co k-edge. The radical distribution functions, the fitting result of bond length and coordination numbers, indicated there was an impurity in the highest Co concentration sample with x = 0.08. Although most of the Co atoms were substituted for Zn sites in ZnO with x = 0.08, a few of Co atoms formed a microstructure similar to Co₃O₄, which was not found in the XRD and HRTEM. The room temperature ferromagnetic behaviour was found for x = 0.01 sample by superconducting quantum interference device .     

Cu-doping effect on structural, optical and photoluminescence properties of Zn0.96−xFe0.04CuxO (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) nanopowders by sol–gel method

Zn_0.96?xFe_0.04Cu_xO (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) nanopowders have been synthesized by sol–gel method. The synthesized samples have been characterized by powder X-ray diffraction, energy dispersive X-ray spectra, X-ray photoelectron spectroscopy, UV–visible spectrophotometer and Fourier transform infrared spectroscopy. The XRD measurement reveals that the prepared nanopowders have different microstructure without changing a hexagonal wurtzite structure. The calculated average crystalline size increases from 20.9 to 22.1 nm for x = 0 to 0.02 then gradually decreases to 18.2 nm for x = 0.10 which were confirmed by SEM and TEM micrographs. The change in lattice parameters, micro-strain, and shift of X-ray diffraction peaks towards lower angles and increase of energy gap reveal the substitution of Cu²⁺ ions into Zn–Fe–O matrix. X-ray photoelectron spectroscopy study described the increase of oxygen vacancies with increase of Cu concentrations, which was found to enhance the green emission. The presence of functional groups and the chemical bonding is confirmed by FTIR spectra. Photoluminescence spectra of Zn_0.96?xFe_0.04Cu_xO system shows that the blue shift in NBE ultraviolet emission from 389 to 369 nm and the same blue shift in green band emission from 552 to 535 nm with enhancing intensity confirms the substitution of Cu into the Zn–Fe–O lattice. Cu-doped Zn_0.96?xFe_0.04Cu_xO system is appreciable for the fabrication of nano-optoelectronic devices like tunable light emitting diode in the near future.     

Ni添加对0.4Zr0.1V1.1Mn0.5Cr0.1合金的相结构和电化学性能的影响

本文通过XRD、SEM、EDS研究了Ti_0.4Zr_0.1V_1.1Mn_0.5Cr_0.1Ni_x(x=0，0.2，0.4，0.6，0.8)合金的相结构和电化学性能。该合金系由BCC结构的V基固溶体主相和六方结构的C14 Laves第二相组成，Ni能够促进第二相的生成，Ni含量的增加导致了各相中的化学组成和晶格参数的变化，并通过电化学方法研究了Ni含量对_0.4Zr_0.1V_1.1Mn_0.5Cr_0.1合金电极的最大放电容量、自放电性能、高倍率放电性能、循环稳定性能等的影响。     

Synthesis and Characterization of Ba0.5Sr0.5NixCo0.8‐xFe0.2O3‐δ (x=0 and 0.2) Perovskites as Electro‐catalysts for Methanol Oxidation in Alkaline Media

In this study, the perovskite‐type oxides Ba_0.5Sr_0.5Ni_0.2Co_0.6Fe_0.2O_3‐δ (BSNCF) with different B‐site transition metal elements were investigated as a new catalyst for methanol oxidation. They were prepared by the partial substitution of cobalt by nickel in Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ (BSCF) sample. Both materials prepared using a combined citrate/EDTA complexing method and their catalytic activitiesfor methanol oxidation were comparativelystudied using cyclic‐voltammetry (CV) and chronoamperometry (CA) in alkaline media at room temperature. Structural, textural, morphological and redox properties of the synthesized solids were investigated by several physicochemical methods such as XRD, FTIR, LRS, SEM‐EDX, BET and H₂‐TPR. The as‐prepared materials were obtained with high purity and high crystallinity. The partial substitution of cobalt by nickel in BSCF perovskite changes the structure of the solid which pass from cubic structure to a mixture of cubic and hexagonal forms. This change is accompanied by an increase in BET surface area and a decrease in crystalline size. For the electro‐catalysis measurements, results demonstrated that partially substituting of Co by Ni in BSCF structure enhance the electro‐catalytical activity towards the oxidation of methanol under alkaline conditions, making it an electro‐catalyst candidate for practical utilization in DMFCs.     

Improvement of magnetoelectric coupling effect in Ba0.8Sr0.2TiO3-Co0.5Cu0.5Fe2O4 multiferroic fluids by tuning the composition

Ba_0.8Sr_0.2TiO₃ (BST) and Cu_0.5Co_0.5Fe₂O₄ (CCFO) nanopowders were prepared by hydrothermal method and chemical coprecipitation, respectively. Barium strontium titanate nanopowder–nano mixed oxides containing copper, cobalt, and iron (BST-CCFO) multiferroic fluids with different mass ratios (m_BST/m_CCFO = 1:2, 1:1, and 2:1) were prepared by using dimethyl silicone oil and silane coupling agent. Effect of mass ratio on the magnetoelectric performance was comparatively investigated. X-ray diffraction (XRD) showed that the BST and CCFO powders had no secondary phases, which are tetragonal perovskite structure and cubic spinel structure, respectively. Scanning electron microscopy (SEM) showed that the average grain size of BST and CCFO was 26.34 nm and 26.82 nm, respectively. The agglomeration of BST nanopowder was serious. Under the external magnetic field, the BST-CCFO multiferroic fluid will form a chain structure due to the directional movement of magnetic particles, thus enhancing the dielectric properties and ferroelectric properties of multiferroic fluid. The chain structure under the action of magnetic field will change the motion of ferroelectric particles, so that the magnetoelectric coupling effect of multiferroic fluid is significantly enhanced, which is much higher than that of the same type of magnetoelectric composite ceramics. This study is expected to provide a new way to improve the magnetoelectric coupling effect of multiferroic materials.     

Hydration and forms of oxygen-hydrogen groups in Oxyfluorides Ba2 ? 0.5x In2O5 ? x F x

A number of fluorine-substituted compounds were synthesized from brownmillerite Ba₂In₂O₅. The homogeneity range of the Ba_{2 ? 0.5x} In₂O_{5 ? x} F _x solid solution (x ?? 0.3) was determined by X-ray diffractometry. The studied phases were found to be able to incorporate water from the gas phase, due to which their orthorhombic structure transforms into tetragonal one. The degree of hydration decreased as the fluorine content in the solid solution increased. As in the case of Ba₂In₂O₅, the energetically nonequivalent hydroxo groups were found to be the main form of oxygen-hydrogen groups.     

Characterization of phase transition of Ba2-xSrxIn2O5 by thermal analysis and high temperature X-ray diffraction

The phase transitions of Ba_2-xSr_xIn₂O₅ were investigated with various thermal analyses and high-temperature X-ray diffraction. It was clarified that crystal structure of Ba_2-xSr_xIn₂O₅ with x=0.0~0.4 varies from brownmillerite through distorted perovskite to another distorted perovskite with increase of temperature. The phase transition from brownmillerite to distorted perovskite was revealed to be first order, whereas transition from distorted perovskite to another one was second order. The specimen with x≥0.5 showed only one first order phase transition from brownmillerite to distorted perovskite. The phase diagram of Ba_2-xSr_xIn₂O₅ was established and existence of tricritical point at ~1100°C with x=0.4~0.5 was suggested. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal stability of the manganese-nickel mixed ferrite and iron phases in the Mn0.5Ni0.5Fe2O4/Fe composite/nanocomposite powder

The composite/nanocomposite powders of Mn_0.5Ni_0.5Fe₂O₄/Fe type were synthesized starting from nanocrystalline Mn_0.5Ni_0.5Fe₂O₄ (D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn_0.5Ni_0.5Fe₂O₄/Fe, were milled for up to 120 min and subjected to heat treatment at 600 °C and 800 °C for 2 h. The manganese-nickel ferrite/iron composite samples were subjected to differential scanning calorimetry (DSC) up to 900 °C for thermal stability investigations. The composite component phases evolution during mechanical milling and heat treatments were investigated by X-ray diffraction technique. The present phases in Mn_0.5Ni_0.5Fe₂O₄/Fe composite are stable up to 400–450 °C. In the temperature range of 450-600 °C, the interdiffusion phenomena occurs leading to the formation of Fe_1?xMn_xFe₂O₄/Ni–Fe composite type. The new formed ferrite of Fe_1?xMn_xFe₂O₄ type presents an increased lattice parameter as a result of the substitution of nickel cations into the spinel structure by iron ones. Further increases of the temperature lead to the ferrite phase partial reduction and the formation of wustite-FeO type phase. The spinel structure presents incipient recrystallization phenomena after both heat treatments (600 °C and 800 °C). The mean crystallites size of the ferrite after heat treatment at 800 °C is about 75 nm. After DSC treatment at 900 °C, the composite material consists in Fe_1?xMn_xFe₂O₄, Ni structure, FeO, and (NiO)_0.25(MnO)_0.75 phases.     

The nature of the orthorhombic to tetragonal phase transition in Sr1−xCaxMnO3

The orthorhombic-tetragonal phase transition in the perovskite series Sr_1−xCa_xMnO₃ 0.4?x?0.6 has been studied by synchrotron X-ray powder diffraction. At room temperature the Ca rich oxides x?0.45 have the orthorhombic Pbnm superstructure whereas Sr_0.6Ca_0.4MnO₃ is two phases with both tetragonal I4/mcm and orthorhombic Pbnm. Analysis of the octahedral tilts suggest the co-existence of these two phases is a consequence of a first-order I4/mcm to Pbnm transition. The evolution of the structure of Sr_0.5Ca_0.5MnO₃ with temperature is also described and this is found to evolve from orthorhombic to tetragonal and ultimately cubic.     

Structural stability and electrochemical properties of Gd-doped ZrO2 nanoparticles prepared by sol–gel

Cubic, tetragonal and monoclinic Gd-doped zirconia nanoparticles with nominal composition Gd_xZr_1?xO₂ in the range 0 ≤ x ≤ 0.2, were prepared by annealing dried gels of Gd-containing zirconia at temperatures over the range between 450 and 1,300 °C. The synthesized zirconia-based nanoparticles with increased gadolinium load were characterized by X-ray powder diffraction, infrared and Raman spectroscopies, and transmission electron microscopy. The stabilization of the crystalline forms of Gd-doped ZrO₂ solid solutions depends on the amount of Gd dopant and the annealing temperature. For low Gd loads in Gd_xZr_1?xO₂ being x < 0.05, the tetragonal form is the single phase up to 1,100 °C, whereas the monoclinic is the crystalline form detected up to 1,300 °C. Within the range of compositions 0.05 ≤ x < 0.1, is the tetragonal the only stabilized zirconia crystalline structure over the whole range of temperature up to 1,300 °C. For higher Gd-contents, in the range 0.1 ≤ x ≤ 0.2, is the cubic zirconia form the only stable phase for the whole range of annealing temperatures. Solid-state electrochemistry of the gadolinium-doped zirconia performed by the voltammetry of microparticles approach allowed distinguishing different electrochemical answers of Gd cation associated with slightly different local coordination surrounding of cations. Enantioselective electrocatalytic effect of monoclinic Gd-doped ZrO₂ on the oxidation of l-(+)-tartaric acid and d-(?)-tartaric was also studied.     

Spektroskopische und strukturelle Untersuchungen an hexagonalen Elpasolithen

Inhaltsübersicht. Es werden die Ergebnisse der röntgenographischen, ligandenfeldspektro-skopischen sowie IR-spektroskopischen Untersuchungen des Mischkristallsystems Sr_2–xBa_xNi TeO₆ mitgeteilt und mit denen entsprechender Untersuchungen der Mischkristalle Ba₂NiTe_xW_1–xO₆ und Ba₂Ni_xMg_1–xTeO₆ verglichen. In diesen Systemen ist mit wachsendem x ein Übergang von der Elpasolith- über die hexagonale BaTiO₃-(6-Schichten-) zur hexagonalen Ba₂NiTeO₆-(12-Schichten-) Struktur zu beobachten. Im Falle der Verbindungen Sr_2–xBa_xNiTeO₆ konnten zusätzlich bei kleinen x-Werten Übergänge von der monoklinen Struktur (Sr₂NiTeO₆) über eine tetragonale Variante der Elpasolithstruktur zum kubischen Gitter gefunden werden. Mittels bei 4 K und 293 K aufgenommener Ligandenfeldspektren wird die Auswirkung der strukturellen Veränderungen beim Ubergang von der geordneten Elpasolithstruktur zu den hexagonalen Varianten auf die Symmetrie und die Bindungsverhältnisse der NiO₆-Oktaeder verfolgt, während die IR-Spektren zusätzlich die Symmetrieverände-rungen der TeO₆-Oktaeder erkennen lassen. Schließlich konnte mit Hilfe beider spektroskopischen Methoden Aussagen über die Kationenverteilung in den hexagonalen Phasen gemacht werden. Spectroscopic and Structural Investigations on Hexagonal Elpasolites The results of X-ray as well as ligand field and i.r. spectroscopic investigations of the mixed crystal series Sr_2–xBa_xNiTeO₆ are reported and compared with those of Ba₂NiTe_xW_1–xO₆ and Ba₂Ni_xMg_1–xTeO₆. In these compounds transitions from the elpasolite to the hexagonal BaTiO₆ (6 layers) and finally to the hexagonal Ba₂NiTeO₆ (12 layers) structure are observed with increasing x. In addition a change from the monoclinic structure (Sr₂NiTeO₆ type) to a tetragonal variant of the elpasolite lattice and finally to the cubic structure is found in the mixed crystal series Sr_2–xBa_xNiTeO₆ at low x values. The influence of these structural changes on the symmetry and the bonding within the NiO₆ polyhedra is studied by the parameters taken from the 4 K and 293 K ligand field spectra. In addition the i.r. spectra give information with respect to the symmetry of the TeO₆ polyhedra. Finally the cation distribution in the hexagonal phases could be deduced from the spectroscopic data.     

Synthesis and properties of colored copper-containing alkaline-earth phosphates with an apatite structure

Colored compounds A₅(PO₄)₃Cu_0.1OH _z , where A = Ba_1-x Sr _x (x=0,0.5,0.8), Sr_1-y Ca _y (y=0,0.2, 0.5, 1), and Ba_1/3Sr_1/3Ca_1/3 with an apatite structure containing copper ions in the hexagonal channels have been synthesized by the thermal treatment of the corresponding carbonates, oxides, and ammonium hydrophosphate at 1150°C. The use of the composition with A = Ba_0.5Ca_0.5 gives a multiphase product containing apatite (Ba_1-x Ca _x )₅(PO₄)₃Cu _y OH _z with x ∼ 0.2 as the major phase. The hexagonal lattice parameters of apatite depend linearly on the content of solid solution in the alkaline-earth metals. In the series of A = Ba, Ba-Sr, Sr, Sr-Ca, and Ca, the color of the samples changes smoothly from blue through violet to pink, whereas the samples with A = Ba_0.5Ca_0.5 and Ba_1-3Sr_1-3Ca_1-3 are light gray. The diffuse reflectance electronic spectra exhibit two absorption bands characteristic of the copper ions in the hexagonal channels. Their positions depend on the alkaline-earth metal content of the compound. The third characteristic band appears in the spectrum of calcium apatite. Its relative intensity increases when calcium is gradually replaced by strontium and especially by barium, which results in worsening and even loss of the sample color. These spectral changes are presumably due to the transition of some copper ions from the hexagonal channels to other positions of the crystal lattice.     

Sol–gel synthesis of nanocrystalline Zn1−xNixFe2O4 ceramics and its structural,magnetic and dielectric properties

Zn_1?xNi_xFe₂O₄ (0.0 ≤ x ≤ 1.0) nanoparticles are prepared by sol–gel method using urea as a neutralizing agent. The evaluation of XRD patterns and TEM images indicated fine particle nature. The average crystallite size increased from 10 to 24 nm, whereas lattice parameters and density decreased with increasing Ni content (x). Infrared spectra showed characteristic features of spinel structure along with a strong influence of compositional variation. Magnetic measurements reveal a maximum saturation magnetization for Zn_0.5Ni_0.5Fe₂O₄ (x = 0.5); however, reduced value of magnetization is attributed to the canted spin structure and weakening of Fe³⁺(A)–Fe³⁺(B) interactions at the surface of the nanoparticles. Impedance analysis for different electro-active regions are carried out at room temperature with Ni substitution. The existence of different relaxations associated with grain, grain boundaries and electrode effects are discussed with composition. It is suggested that x = 0.5 is an optimal composition in Zn_1?xNi_xFe₂O₄ system with moderate magnetization, colossal resistivity and high value of dielectric constant at low frequency for their possible usage in field sensor applications.     

Synthesis and structural studies of Sr2Co2−xAlxO5, 0.3⩽x⩽0.5

Sr₂Co_2−xAl_xO₅, 0.3⩽x⩽0.5, with a perovskite related structure has been synthesized. The XRD powder patterns showed reflections from the basic cubic perovskite structure along with some additional weak superstructure reflections. Electron diffraction (ED) and high-resolution transmission electron microscopy (HRTEM) studies show that crystallites of Sr₂Co_2−xAl_xO₅ consist of small intergrown differently oriented domains, about 40 Å in diameter, with brownmillerite structure.     

Oxygen permeation and phase structure properties of partially A-site substituted BaCo0.7Fe0.225Ta0.075O3-δ perovskites

Ba_0.9R_0.1Co_0.7Fe_0.225Ta_0.075O_3-δ (BRCFT, R = Ca, La or Sr) membranes were synthesized by a solid-state reaction. Metal cation Ca²⁺, La³⁺ or Sr²⁺ doping on A-site partially substituted Ba²⁺ in BaCo_0.7Fe_0.225Ta_0.075O_3-δ oxides, and its subsequent effects on phase structure stability, oxygen permeability and oxygen desorption were systematically investigated by XRD, TG-DSC, H₂-TPR, O₂-TPD techniques and oxygen permeation experiments. The partial substitution with Ca²⁺, La³⁺ or Sr²⁺, whose ionic radii are smaller than that of Ba²⁺, succeeded in stabilizing the cubic perovskite structure without formation of impurity phases, as revealed by XRD analysis. Oxygen-involving experiments showed that BRCFT with A-site fully occupied by Ba²⁺ exhibited good oxygen permeation flux under He flow, reaching about 2.3 mL·min⁻¹ ·cm⁻² at 900 °C with 1 mm thickness. Of all the membranes, BLCFT membrane showed better chemical stability in CO₂, owing to the reduction in alkalinity of the mixed conductor oxide by La doping. In addition, we also found the stability of the perovskite structure under reducing atmospheres was strengthened by increasing the size of A-site cation (Ba²⁺>La³⁺>Sr²⁺>Ca²⁺).     

Hydrothermal synthesis, structure and property of nano-BaTiO3-based dielectric materials

A series of Ba_1-xSr_xTi_1-yZr_yO₃ (0≤x≤0.5, 0≤y≤0.4) and BA_1?xZn_xTi_1?ySn_yO₃ (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr²⁺ and Zr⁴⁺ or Zn²⁺ and Sn⁴⁺ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO₃ phase at room temperature.     

Analysis of the phase composition and homogeneity of ferrite lithium-substituted powders by the thermomagnetometry method

In the present work, the possibilities of application of the thermomagnetometry TG(M)/DTG(M) method for estimation of the phase homogeneity of end products of synthesis at different stages of ferritizing annealing are considered on the example of solid-state synthesis of Li_0.5(1?x)Fe_2.5?0.5xZn_xO₄ and Li_0.5(1 + x)Fe_2.5?1.5xTi_xO₄ (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) lithium-substituted ferrospinels. Results of thermomagnetometric analysis are compared with XRD data. It is shown that the resolution of the TG(M)/DTG(M) method on two orders exceeds capabilities of the traditional XRD method. Considerable influence of both intermediate grinding and mixing of samples and concentration of an inducted impurity on the homogeneity of the synthesized powders is confirmed.     

High-temperature studies of La1−x SrxFeO3−δ solid solutions using synchrotron radiation

A series of La_1?x Sr_xFeO_3?δ samples with a perovskite structure were investigated by high-temperature X-ray analysis using synchrotron radiation. In this series, one can observe a morphotropic phase transition (0.3 ? x ? 0.4) from the orthorhombic (0 ? x < 0.3) to cubic (0.4 < x ? 0.75) modification. The samples from the morphotropic transition region (MTR) at room temperature have a highly disordered microblock structure related to their phase heterogeneity; according to high-temperature X-ray analysis data, this is the result of particle stratification of the high-temperature homogeneous solid solution formed at the temperature of the synthesis (1200°C) in the course of cooling.     

Phase segregation in the Gd1−xSrxFeO3−δ series

Gd_1−xSr_xFeO_3−δ ferrites have been studied by means of X-ray powder diffraction in the whole composition range. Single-phase solid solution is found for x<0.09 and for x>0.63. At intermediate Sr content, phase segregation takes place. Compounds with x?0.05 crystallize in the orthorhombic structure, space group Pbnm. Oxygen-deficient Gd_1−xSr_xFeO_3−δ with x?2/3 are cubic or nearly cubic. The oxygen vacancies stabilize the cubic phase for x=2/3 whereas highly oxidized samples show an orthorhombic distortion, which has not been observed earlier. Magnetic and electrical properties have been measured for the single-phase solid solutions. Gd_1−xSr_xFeO_3−δ compounds with x?2/3 order antiferromagnetically below ∼100 K. In the paramagnetic region, their susceptibility follows the Curie-Weiss law in all but SrFeO_2.96 compound. These ferrites show semiconducting behavior in the electrical transport likely related to atomic disorder. We find that the conductivity activation energy becomes larger by increasing either the Gd content or the oxygen vacancies.