用Mssbauer谱研究Zn_2SnO_4的湿敏机理

本文用 Mssbauer 谱学方法,对半导体陶瓷 Zn_2SnO_4的湿敏机理做了分析,得出结论:Sn 原子对Zn_2SnO_4的湿敏机理是有贡献的,Zn_2SnO_4湿敏机理是电子离子混合型传导,作为湿敏机理分析方法,M(?)ssbauer 谱是比较合适的。     

Atom Probe and Mssbauer Spectroscopy Investigations of Cementite Dissolution in a Cold Drawn Eutectoid Steel

Mssbauer spectrum and three dimensional atom probes(3DAP) were combined to investigate the mechanism of cementite dissolution in a cold-drawn eutectoid steel at a true strain of 2.89.The experimental results suggest that the dislocations play an important role in the dissolution of the cementite by sweeping across the nano-scaled cementite,and transferring carbon from cementite to ferrite inducing cementite decomposition.The mechanism of cementite dissolution in the steel is discussed in association with t...     

Dy(Fe,M)_(12)(M=Si,Ti,V)合金的Mssbauer谱学研究

DyFe_(10)Si_2合金的~(57)Fe变温Mssbauer谱学研究,发现温度在210K处,超精细场随温度有不连续变化。此温度对应于合金的自旋重取向温度。Si,Ti和V作为形成ThMn_(12)型结构的稳定化元素,造成各相应合金的自旋重取向温度有一些差别。分析了Si,Ti和V元素造成合金磁晶各向异性差别的原因,它使得DyFe_(10)V_2,DyFe_(11)Ti和DyFe_(10)Si_2合金的自旋重取向温度不同。DyFe_(10)Si_2合金的8i晶位四极劈裂在温度210K处改变符号。     

ZnFe2O4纳米结构制备及其M(o)ssbauer谱分析

通过水解Zn/Fe3O4纳米粒子制备ZnFe2O4纳米结构,采用XRD和TEM检测产品的成分和形貌变化,验证反应过程方程的正确性.结果表明:当反应温度为260℃时,产品中含有ZnO纳米棒,随着反应温度升至300℃,ZnO纳米棒逐渐消失,得到纯度较高的ZnFe2O4纳米颗粒,粒度分布在20～30nm范围内.产品的M(o)...     

纳米Mn_(0.4)Zn_(0.6)Fe_2O_4磁流体的制备与粘度特性

为了得到性能稳定的磁流体,采用水热法制备Mn_(0.4)Zn0.6Fe_2O_4磁流体,使用毛细法粘度计测量磁流体的粘度,分析磁流体粘度的影响因素。结果表明:磁流体的粘度随着磁性粒子体积分数的增大而增大,且外加磁场的作用会加快增大的趋势;磁流体磁性粒子体积分数不变时,表面活性剂质量分数越大粘度也越大,当表面活性剂质量分数小于4%时,粘度增加呈线性趋势;外加磁场强度越大,粘度也越大;无论外界环境有无磁场作用,磁流体的粘度都随着温度的升高而减小,温度的升高还会减弱外加磁场对磁流体粘度的影响。     

Influence of Microwave Radiation on Properties and Structure of Fe_2O_3/SO_4~(2-) Solid Superacid Catalyst

The microwave radiation method was introduced to prepare the Fe_2O_3/SO solid superacid.Its structure and properties were investigated by means of X-ray diffraction and infrared spectrum analyses as well as measurement of magnetic susceptibility and rate of esterification. The structure of the superacids prepared in microwave field can be crystalline or non-crystalline, the latter has not been reported yet in literatures. Comparing with the traditional superacid, the non-crystalline Fe2O3/SO superacid prepared in microwave field has the highest magnetic susceptibility and catalytic activity. The di-coordination of Fe2O3 and SO and the S=O bi-bond were reinforced by microwave radiation, which is favorable for increasing the acid intensity of the Fe2O3/SO catalyst     

Preparation, Structure, and Properties of (Bi,Pb)2Sr2Ca2Cu3O10 + δ Ceramics with Si3N4 Additions

The microstructure, phase composition, texture, and superconducting properties (T _c, T _c, j _c(T), and R(T) at H= 0 and 5 mT) of (Bi,Pb)₂Sr₂Ca₂Cu₃O_{10 +} ceramics (sintering at 840°C for 36 h) with ultrafine Si₃N₄ additions (0.05–0.2 wt %) are studied. The introduction of 0.05–0.1 wt % Si₃N₄ is shown to reduce the width of the superconducting transition by 2–3 K and to raise the critical current density at temperatures below 95 K.     

Structure and Diamagnetic Properties of (Pb0.6SnyCu0.4 ? y)Sr2(Y1 ? xCax)Cu2Oz

The effect of Sn doping in (Pb_0.6Sn _y Cu_{0.4 – y} )Sr₂(Y_{1 – x} Ca _x )Cu₂O _z with 0 y 0.3 and 0 x 0.7 was investigated. It was established that a nearly pure 1212 phase can be obtained at 0 y 0.1 and 0 x 0.3. The obtained XRD patterns as well as the results of the EDX and ICP-AES analyses showed that Sn substitution is possible in the (Pb,Cu)-1212 phase. Superconductivity was observed at 0.4 x 0.7. The onset of the diamagnetic transitions varied from 10 to 30 K. The influence of the strong Pb deficiency on the superconducting properties of the samples was discussed.     

Effect of Hydrogen on the Structure and Magnetic Properties of (Sm1–xErx)2Fe17 (x = 0.1, 0.4) Solid Solutions

Inorganic Materials - (Sm1–xErx)2Fe17 (x = 0.1, 0.4) solid solutions have been prepared by induction melting and then hydrided to give high hydrogen content materials: Sm1.8Er0.2Fe17H4.4 and...     

Nanocrystalline NiFe2O4 and nanocomposites of (NiFe2O4)(1-x)(Al2O3)x (x = 0.25, 0.40): superparamagnetic behavior and Mössbauer spectroscopy

Nanocrystalline NiFe2O4 with different particle sizes and nanocomposites of (NiFe2O4)(1-x)(Al2O3)x (x = 0.25, 0.40) were prepared by using co-precipitation method. In this method two techniques viz., 'ultrasonication' and 'magnetic stirring' during co-precipitation were used. The as prepared samples were annealed at different temperatures to obtain samples with different particle sizes. The formation of the nanocrystalline spinel phases of all the samples were confirmed by X-ray diffraction (XRD) patterns. The sizes of the nanoparticles of all the samples were calculated from the broadening of the (311) line in the XRD pattern. The distribution of sizes are remarkably less in samples obtained from 'ultrasonication' technique compared to those obtained in 'magnetic stirring' technique. The different soft magnetic quantities viz., coercive field, magnetization, remanance, hysteresis losses etc. were extracted from the ac hysteresis loops observed at different frequencies. The variations of coercive field and hysteresis loss as functions of frequency and particle sizes have been studied. M?ssbauer spectra of the samples along with the hysteresis loops recorded at room temperature indicate the presence of superparamagnetic (SPM) relaxations of the nanoparticles. Also, SPM relaxations have been introduced in the samples annealed at higher temperature by encapsulating the nanoparticles in non-magnetic matrix of Al2O3 with 40% coating.     

Crystal Structure,Luminescence, and Thermodynamic Properties of Pb10 – xEux(GeO4)2 + x(VO4)4 – x (x = 0.1, 0.2, 0.3) Substituted Apatites

Inorganic Materials - Pb10 – xEux(GeO4)2 + x(VO4)4 – x (x = 0.1, 0.2, 0.3) Eu-substituted lead germanatovanadates with the apatite structure have been prepared by solid-state reactions,...     

Structure,chemical stability and electrical conductivity of perovskite La0.6Sr0.4M0.3Fe0.7O3−δ (M = Co,Ti) oxides

The perovskite La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) powders have been synthesized by the citrate gel method. The structural and chemical stability of the La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) oxides were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques. The electrical conductivities of the sintered La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) ceramics were measured. The results demonstrate the chemical stability in H₂/helium (He) atmosphere of the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3?δ oxide is improved significantly compared to that of the La_0.6Sr_0.4Co_0.3Fe_0.7O_3?δ oxide. The incorporation of Ti^3+/4+ ions in the perovskite structure can significantly stabilize the neighboring oxygen octahedral due to the stronger bonding strength, leading to the enhanced structural and chemical stability of the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3?δ. In addition, the perovskite La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) oxides possess much higher chemical stability in CO₂/He atmosphere than that of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ oxide, in which the perovskite structure is destroyed completely in a flowing CO₂-containing atmosphere.     

Structure Stability and Oxygen Permeability of Perovskite-type Oxides of Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.1)R_(0.1)O_ (3-δ)(R=Al,Mn,Fe,Ce,Cr,Ni,Co)

Perovskite-type Ba 0.5 Sr 0.5 Co 0.8 Fe 0.1 R 0.1 O 3 δ (R=Al,Mn,Fe,Ce,Cr,Ni,Co) oxide membranes were exploited and synthesized.Oxygen behavior,order-disorder transition and phase stability of these composite oxides were investigated by combined analysis of X-ray diffraction (XRD),temperature programmed desorption (TPD),thermogravimetric-differential thermal analysis (TG-DTA).Oxygen permeation through these membranes was studied by the gas chromatography (GC) method using a high-temperature permeation cell in a wide temperature range from 700 to 950 C.High permeation fluxes were observed for these materials.The high permeation flux was about 3.19 ml·min 1 ·cm 2 under air/He gradients at 950 C,which was achieved for Ba 0.5 Sr 0.5 Co 0.8 Fe 0.1 Ni 0.1 O 3 δ (BSCFNiO) membrane.The results of analysis showed no phase transition for BSCFNiO oxide with increasing temperature and XRD pattern of this material after O 2-TPD indicated to sustain a pure perovskite structure after oxygen permeation process.     

Synthesis of Double Uranyl Phthalates of the M4[(UO2)4(μ3-O)2(C6H4C2O4)4] ⋅ nH2O Type with M = NH4, K, and Cs. Crystal Structure of K4[(UO2)4O2(C6H4C2O4)4] ⋅ 3H2O

Double U(VI) phthalates with NH ₄ ⁺ , K⁺, and Cs⁺ ions in the outer sphere were synthesized. The X-ray phase analysis shows that their structures are similar. Single crystals were prepared and the structure of K₄[(UO₂)₄(μ₃-O)₂(C₆H₄C₂O₄)₄] ? 3H₂O was solved. In the [(UO₂)₄O₂(C₆H₄C₂O₄)₄]^4? anions forming the main structural motif, each bridging oxygen atom μ₃-O combines one pentagonal and two hexagonal bipyramids, which, in turn, are combined in centrosymmetrical tetramers. The phthalate ions have coordination capacity equal to 3; each ligand coordinates U(1) in the bidentate fashion via one carboxy group and U(2) in the bidentate fashion to form a planar seven-membered chelate ring.     

Effect of Synthesis Conditions on the Lithium Nonstoichiometry and Properties of La2/3 – x Li3x □4/3 – 2x M2O6 (M = Nb, Ta) Perovskite-like Solid Solutions

The effects of the nominal composition and synthesis conditions on the lithium nonstoichiometry of La_{2/3 – x} Li_{3x 4/3 – 2x} Nb₂O₆ (I) and La_{2/3 – x} Li_{3x 4/3 – 2x} Ta₂O₆ (II) solid solutions are studied. The results demonstrate that lithium losses can be reduced from 26–30 to 14–15 mol % in system I and from 15 to 4 mol % in system II. It is shown that the disturbance of electroneutrality caused by Li nonstoichiometry in the solid solutions is eliminated via the formation of oxygen vacancies in positions O(1) (1f: 1/2 1/2 0) and O(2) (1h: 1/2 1/2 1/2) of the cation-deficient perovskite structure. The optimal lithium ion conductivity is offered by solid solutions with /3x 2.6 and x 0.136–0.143.     

Synthesis of M(NpO<Subscript>4</Subscript>)<Subscript>2</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O (M = Mg,Ca, Sr,Ba) Using Н<Subscript>3</Subscript>ВО<Subscript>3</Subscript> Solutions and Properties of These Salts

Two procedures for preparing the compounds M(NpO₄)₂·nH₂O (M = Mg, Ca, Sr, Ba) using boric acid were suggested. In the first procedure, samples of freshly prepared salts M₃(NpO₅)₂·nH₂O (M = Ca, Sr, Ba) are treated with excess 0.5 M H₃BO₃ with vigorous stirring. In the process, the initially light green salts rapidly transform into black products of the general composition M(NpO₄)₂·nH₂O. In the second procedure, a measured volume of a Np(VII) solution with a known LiOH concentration was added to excess 0.5 M H3BO3 solution containing a calculated amount of Mg, Ca, Sr, or Ba nitrate. The reaction yields black precipitates of the same compounds as in the previous case. After washing with water and drying in an oxygen stream, the final products contain a small impurity of Np(VI). The IR spectra suggest that the compounds obtained are structurally related to the previously studied salts MNpO₄ (M = K–Cs), i.e., in their lattices there are neptunium–oxygen layers built of NpO₂³⁺ cations and bridging O atoms. New data on the properties of the compounds M₃(NpO₅)₂·nH₂O with M = Ca, Sr, and Ba were also obtained.