非晶态Fe13.3Ni69.6B16.2Si0.9的结构驰豫

本文讨论了非晶合金Fe_13.3Ni_69.6B_16.2Si_0.9的结构弛豫动力学及可逆弛豫过程,研究了各种热处理引起居里温度T_c的变化。发现经长时间退火后T_c趋于平衡值且动力学可通过弛豫时间连续谱加以描述。可逆弛豫过程可用CSRO来说明,并且某一物理量的可逆变化并不意味着整个结构的变化是可逆的。 关键词：     

纳米复合永磁Pr9Fe74Co12B5Snx(x=0, 0.5)的磁化行为与磁黏滞性

用熔体快淬法制备了纳米复合永磁样品Pr₉Fe₇₄Co₁₂B₅ 与Pr₉Fe₇₄Co₁₂B₅Sn_0.5，分析了样品的起始磁化、反磁化过程，测得样品的总磁化率、可逆磁化率以及样品的磁黏滞性.结果表明，两样品在室温下均表现为单一硬磁相磁化行为，在低温下表现为双相行为，且由于添加Sn后使晶粒均匀化从而导致样品低温下的双相行为更加明显.添加Sn后引起样品中软磁相含量和软磁相晶粒尺寸的增加，使磁化反转中可逆磁化部分增多，且使反磁化形核场降低.磁黏滞性研究表明，热激活体积与软磁相晶粒的大小有关. 关键词： 纳米复合永磁 磁化反转 磁粘滞     

Synthesis and electrochemical performances of Li4Ti4.95Al0.05O12/C as anode material for lithium-ion batteries

Spinel compounds Li₄Ti_5−xAl_xO₁₂/C (x=0, 0.05) were synthesized via solid state reaction in an Ar atmosphere, and the electrochemical properties were investigated by means of electronic conductivity, cyclic voltammetry, and charge-discharge tests at different discharge voltage ranges (0-2.5 V and 1-2.5 V). The results indicated that Al³⁺ doping of the compound did not affect the spinel structure but considerably improved the initial capacity and cycling performance, implying the spinel structure of Li₄Ti₅O₁₂ was more stable when Ti⁴⁺ was substituted by Al³⁺, and Al³⁺ doping was beneficial to the reversible intercalation and deintercalation of Li⁺. Al³⁺ doping improved the reversible capacity and cycling performance effectively especially when it was discharged to 0 V.     

High temperature phase transition in NH4H2PO4

NH₄H₂PO₄ (ADP) has been investigated by infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis and d.c. conductivity in the temperature range of 25–180° C. Sharp reversible changes were observed in the region from 400 to 500 cm^?1 of the infrared spectra in the temperature range of 138–174° C. Similar and supportive data were obtained with DSC, TGA and DC conductivity measurements. The results clearly suggest a high temperature phase transition for ADP before its melting point.     

The reversible photostructural change studied by ESR of Mn2+ in As2Se3 films

The reversible photostructural change is studied from a microscopic point of view using ESR of Mn²⁺ doped in As₂Se₃ films. It is observed that the hyperfine structure constant changes reversibly corresponding to the reversible optical absorption edge shift. The result is explained in terms of increasing randomness by photoirradiation.     

Metastable complex defects in α-(Al0.02In0.98)2Se3

The electrical properties of α-(Al_0.02In_0.98)₂Se₃ were investigated. In contrast to In₂Se₃, which is characterized by a high and constant concentration of donorlike defect centers, the concentration of active donors in α-(Al_0.02In_0.98)₂Se₃ can be changed in a reversible manner over four orders of magnitude by thermal treatment. To explain this strange behavior, we have proposed a simple model, which presumes formation of complex defect centers consisting of Al atoms at cation sites and native donors.     

Reversible photo-induced volume changes in evaporated As2S3 and As4Se5Ge1 films

Reversible photo-induced volume changes have been observed accompanying reversible optical absorption edge shift produced by successive cycles of band gap illumination and annealing for well-annealed evaporated As₂S₃ and As₄Se₅Ge₁ films. The As₂S₃ film shows an increase in its volume by illumination, while As₄Se₅Ge₁ film shows a decrease. Qualitative discussion has been given in connection with pressure-induced optical constant change.     

快淬Nd3.6Pr5.4Fe83Co3B5薄带的反磁化行为和磁黏滞性

用电弧熔炼法制备了Nd_3.6Pr_5.4Fe₈₃Co₃B₅合金铸锭,然后利用熔旋快淬法在铜辊转速V=20m/s下制备了Nd_3.6Pr_5.4Fe₈₃Co₃B₅薄带.快淬带主要由软磁相α-Fe和Nd₂Fe₁₄B型的硬磁相组成.采用直流退磁剩磁曲线方法分析了样品在反磁化过程中的可逆与不可逆磁化部分,并研究了软磁相和硬磁相的反磁化行为,得到样品的不可逆磁化形核场H_no约为440kA/m.同时研究了样品的磁黏滞性,结果表明由于软磁相的存在使得热激活体积较大. 关键词：     

Magnetic properties and magnetocaloric effects in Tb6Co1.67Si3 compound

Magnetic properties and magnetocaloric effects of Tb₆Co_1.67Si₃ have been investigated by magnetization measurement. This compound is of a hexagonal Ce$_{6}$Ni$_{2}$Si$_{3}$-type structure with a saturation magnetization of 187\,emu/g at 5\,K and a reversible second-order magnetic transition at Curie temperature $T_{\rm C} = 186$\,K. A magnetic entropy change $\Delta S = 7$\,J\,$\cdot$\,kg$^{-1}$\,$\cdot$\,K$^{-1}$ is observed for a magnetic field change from 0 to 5\,T. A large value of refrigerant capacity (RC) is found to be 330\,J/kg for fields ranging from 0 to 5\,T. The large RC, the reversible magnetization around $T_{\rm C}$ and the easy fabrication make the Tb₆Co_1.67Si₃ compound a suitable candidate for magnetic refrigerants in a corresponding temperature range.     

电脉冲对多晶La0.7Ca0.3MnO3比热的影响

对电脉冲诱导的不同电阻态下La_0.7Ca_0.3MnO₃样品的比热进行了研究.实验结果表明,电脉冲导致La_0.7Ca_0.3MnO₃样品比热随电阻状态发生可逆变化.比热随电阻状态的减小而减小.低温比热拟合及不同电阻状态下的比热差与温度关系说明,声子对比热的贡献不随电阻状态变化,磁性和载流子对比热的贡献是导致La_0.7Ca_0.3MnO₃样品比热变化的原因.电脉冲诱导O离子沿一维扩展性缺陷的电化学迁移,导致材料中局部区域的O离子浓度发生变化.O离子浓度的变化导致载流子浓度的变化,同时载流子浓度的变化将使得低温下磁性耦合强度发生变化,从而导致比热发生变化.     

Effect of severe plastic deformation by torsion on the properties and structure of the Ni54Mn21Ga25 and Ni54Mn20Fe1Ga25 alloys

The effect of one-percent substitution of iron for manganese on the physical (magnetic, electrical, thermal, and galvanomagnetic) properties and the crystal structure of the Ni₅₄Mn₂₁Ga₂₅ alloy has been investigated. It has been demonstrated that the deviation of the alloy composition from the stoichiometric composition Ni₅₀Mn₂₅Ga₂₅ leads to the formation of a mixed ferromagnetic-antiferromagnetic state. The atomic disordering and nanostructuring of the alloys under investigation due to the severe plastic deformation by torsion in Bridgman anvils to sizes of 10–20 nm result in the suppression of reversible magnetically controlled shape memory effects.     

Ga30Sb70/Sb80Te20纳米复合多层薄膜的相变特性研究

采用磁控二靶(Ga₃₀Sb₇₀和Sb₈₀Te₂₀)交替溅射方法制备了新型Ga₃₀Sb₇₀/Sb₈₀Te₂₀纳米复合多层薄膜, 对多层薄膜周期中Ga₃₀Sb₇₀层厚度对相变特性的影响进行了研究. 结果表明, 多层薄膜的结晶温度可以通过周期中Ga₃₀Sb₇₀层厚度进行调节, 且随着Ga₃₀Sb₇₀层厚度的增加而升高. Ga₃₀Sb₇₀/Sb₈₀Te₂₀纳米复合多层薄膜的光学带隙随Ga₃₀Sb₇₀层厚度的增加而增大. 采用皮秒激光脉冲抽运光探测技术研究了多层薄膜的瞬态结晶动力学过程, 利用不同能量密度的皮秒激光脉冲可以实现Ga₃₀Sb₇₀/Sb₈₀Te₂₀多层薄膜非晶态和晶态的可逆转变.     

Molar heat capacity of a vitreous solid electrolyte: Ag7I4AsO4

Vitreous solid electrolytes occupy an interesting position between crystalline solid electrolytes and molten salts. In the present work, measurements of the molar heat capacity of vitreous Ag₇I₄AsO₄ indicate that the anion sublattice may become progressively disordered in a reversible manner at temperatures well below the glass-liquid transition temperature. The effect of this on the silver ion mobility is briefly discussed.     

Thermoelectric power of (Me4N)2Ag13I15 and (Et4N)2Ag13I15

Thermoelectric power using reversible silver electrodes and electrical conductivity on the compressed pellets of (Me₄N)₂Ag₁₃I₁₅, and (Et₄N)₂Ag₁₃I₁₅ have been measured between room temperature and below 160°C. The results of θ can be expressed by the equations:?θ = 0.115 (10³/T)+0.2905VK^?1 and ?θ = 0.150 (10³/T) + 0.305mV K^?1; and those of conductivity by the equations; σ = 28.7 exp (?0.17eV/kT) ohm^?1cm^?1 and $\text{σ = 216.6 exp (?0.24e}\text{V}\text{kT}\text{)}$ ohm^?1cm^?1; respectively for Me- and Et-electrolytes. The results are discussed and compared with those of previous authors.     

In-situ strain effect on extrinsic transport of polycrystalline La0.7(Ca,Sr)0.3MnO3 films

The spin-polarised transport in ferromagnetic polycrystalline La_0.7(Sr,Ca)_0.3MnO₃ films on piezoelectric substrate has been investigated. The systematic study involved in finding the effect of in-situ strain on extrinsic electrical transport of various thick polycrystalline La_0.7(Sr,Ca)_0.3MnO₃ thin films. The in-situ strain in the manganite polycrystalline thin film is achieved by applying an electric field to the piezoelectric substrate 0.72 Pb(Mg_1/3Nb_2/3)O₃-0.28 PbTiO₃ (PMN-PT). A reversible strain of about 0.11% is acquired with an application of 10 kV/cm to the piezoelectric substrate. A typical drop in resistance at low magnetic fields has been found in all the polycrystalline manganite films. The effect of reversible strain versus the resultant strain gauges was discussed in all the polycrystalline films. At low temperatures, the effect of strain on low-field magnetoresistance and high-field magnetoresistance was found to be negligible. Further, the results are compared with the transport in manganite films deposited on step edge junctions.     

Elucidation of 3D-to-2D transformation by magnetization studies for Hc in Bi2Sr2CaCu2O8

New magnetization results (for Hc) on a single crystal of Bi2212 elucidating the transition from a one-component to a two- component response across the 3D-to-2D transformation are reported. The two-component response is identified to emanate from the 2D planes and interplanar links. The magnetization response above the transformation temperature T_s and very close to T_c is found to be irreversible in contrast to the reversible behavior so far believed in. A new phase diagram for the mixed state of layered superconductors near T_c is proposed.     

Versatile functionalization of Fe3O4 nanoparticles via RAFT polymerization and click chemistry

Azide-functionalized chain transfer agent (CTA) was synthesized and subsequently employed to mediate the reversible addition fragmentation transfer (RAFT) polymerization of poly(ethylene glycol) monomethacrylate (PEGMA) on the alkyne-functionalized Fe₃O₄ nanoparticles surface together with click chemistry. In a single pot procedure, azide-functionalized CTA, alkyne-functionalized Fe₃O₄ and PEGMA were combined to produce the desired product. Fourier transformed infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) results showed that PEGMA chains were grafted to Fe₃O₄ nanoparticles using RAFT polymerization and click chemistry.     

Structural characterization,thermal, vibrational properties and molecular motions in perovskite-type diaminopropanetetrachlorocadmate NH3(CH2)3NH3CdCl4 crystal

The work presents a detailed analysis of the sequencing of the structural phase transitions in NH₃(CH₂)₃NH₃CdCl₄ crystal by differential scanning calorimetry (DSC), X-ray, infrared, far infrared and Raman spectroscopy. DSC studies have shown that in analyzed crystal occurring one reversible continuous phase transition at 375/374 K (on heating/cooling). Observed in Nujol and Fluorolube mulls in the wide temperature range between 296 K and 413 K spectral changes through the structural phase transition can be attributed to an onset of motion of cations. An assignment of some bands due to internal modes has been also proposed.     

Unusual resistive switching induced by voltage in La0.7Sr0.3MnO3 thin films

The hysteretic and reversible resistive-switching effect was observed in La_0.7Sr_0.3MnO₃ films at room temperature. The resistive switching was found to be most obvious in films fabricated at 30 Pa oxygen pressure, and more distinct in films fabricated on SrTiO₃ substrates than those fabricated on LaAlO₃ substrates. Moreover, La_0.7Sr_0.3MnO₃ films fabricated at a certain oxygen pressure with indium electrodes showed double ‘8’ type current-voltage loops. Some of the results are explained by considering the influence of the interface effect, electrodes and oxygen vacancies, but the mechanism of the double ‘8’ type current-voltage loops remains an open question.     

Electrostatic spray deposition of spinel Li4Ti5O12 thin films for rechargeable lithium batteries

Spinel Li₄Ti₅O₁₂ thin films are important for the fabrication of rechargeable lithium microbatteries. Porous thin films of Li₄Ti₅O₁₂ were prepared by electrostatic spray deposition (ESD) technique with lithium acetate and titanium butoxide as the precursors. The structures of these films were analyzed by scanning electron microscopy and X-ray diffraction. Coin-type cells with a liquid electrolyte were made with the Li₄Ti₅O₁₂ films against metallic lithium. Their electrochemical performance was investigated by means of galvanostatic cell cycling, cyclic voltammetry and Ac impedance spectroscopy. It was found that pure spinel phase of Li₄Ti₅O₁₂ was obtained. After annealing at the optimal temperature of 700 °C, the films can deliver a reversible specific capacity of about 150 mAh/g with excellent capacity retention after 70 cycles. Their electrochemical characteristics were quite comparable with those of the Li₄Ti₅O₁₂ laminate electrodes containing carbon black additive.