Structure and Magnetic Properties of Magnetostrictive FeGa Film on Single-Crystal(100) GaAs and(001) Si Substrate Fabricated by Pulsed Laser Deposition

FeGa thin film has been deposited on(100)-oriented GaAs and(001)-oriented Si substrates with different film thicknesses and laser energy densities at room temperature by pulsed laser deposition system.Materials structure and static magnetic of FeGa film have great changes depending on the substrate and energy density of pulsed laser.X-ray diffraction reveals the presence of first-order order–disorder structure ofgrain phase and disordered bcc A2 structure on GaAs substrate.The coercivity and remanence of FeGa film on GaAs substrate ratio show a regular dependence on the thickness and energy densities.However,film on Si substrate did not exhibit structure change,which can be attributed to a large lattice mismatch between FeGa and Si.     

Magnetoelectric properties of Fe-Ga/BaTiO3 laminate composites

Magnetostrictive and piezoelectric laminate composites of Fe-Ga and BaTiO₃ have been studied. The magnetoelectric (ME) coefficients have been characterized for the transversely magnetized and transversely polarized transverse-transverse (TT) mode. At lower frequencies, the ME voltage coefficient of the laminate was 12.5 mV/Oe. Near the natural resonant frequency (∼95 kHz) of the laminate, the ME voltage coefficient was found to be dramatically increased to 28.5 mV/Oe. In addition, the induced ME voltages were near linear functions of AC magnetic field.     

Structural ordering and magnetic properties of arc-melted FeGa alloys

X-ray diffraction, Mössbauer spectrometry and magnetic properties have been performed on FeGa arc-melted binary alloys in order to study the compositional dependence of the structural ordering and magnetic properties of these alloys. The average magnetic hyperfine field at 300 K decreases with increasing Ga content as does the average magnetic moment per Fe atom, and a linear dependence between both quantities is found for Ga content up to 20 at%. The substitution of Fe by Ga atoms increases the lattice parameter and causes a change in the order of the crystal structure that has been modelled using a binomial distribution method. The effect of Ga atoms as near neighbours of Fe on the average magnetic hyperfine field is evaluated.     

Study of ac impedance spectroscopy of Al doped MnFe2−2xAl2xO4

We have reported electrical properties of Al doped MnFe₂O₄ ferrite using ac impedance spectroscopy as a function of frequency (42 Hz to 5 MHz) at different temperatures (300–473 K). XRD analysis shows that all the compositions are single phase cubic spinel in structure. The complex impedance analysis has been used to separate the grain and grain boundary resistance of MnFe_2−2xAl_2xO₄. From the analysis of impedance spectra it is found that the real (Z′), and imaginary (Z″) part of the impedance decrease with increasing frequency and both are found to decrease with Al doping up to 20%, and thereafter, these increase with further increasing the Al concentration. Experimental results have been fitted with two parallel RC equivalent circuits in series.     

CoFe_2O_4-BaTiO_3颗粒复合材料的频率相关电磁性能

通过湿法球磨制备CoFe2O4-BaTiO3颗粒复合材料,研究材料成分和调制频率与电磁效应的关系。结果表明：电磁效应系数随着调制频率由400Hz增加到1000Hz而增加。由于CoFe2O4的电导率在400-1000Hz范围内对频率敏感,电磁效应的曲线特性而发生改变。在烧结过程中形成第三相Ba2Fe2O5,从而导致电磁效应的下降。     

Electrical, magnetic, and magnetoelectric characterization of fine-grained Pb(Zr0.53Ti0.47)O3-(Ni0.5Zn0.5)Fe2O4 composite ceramics

Fine-grained Pb(Zr_0.53Ti_0.47)O₃-(Ni_0.5Zn_0.5)Fe₂O₄ (PZT-NZFO) magnetoelectric (ME) composite ceramics were fabricated by a modified hybrid process at a low sintering temperature of 900 °C. Well-controlled crystallized grain size and homogeneous microstructure with a good mixture of two phases were observed in the ceramics. The ceramics show coexistence of ferrimagnetic and ferroelectric phases with well-formed ferromagnetic and ferroelectric hysteresis loops at room temperature. A significant ME effect was observed with a ME coefficient of 0.537 V cm⁻¹ Oe⁻¹ in the vicinity of electromechanical resonance. In addition, high capacitance can be obtained at low frequency, and magnetic properties in the ceramics can be tailored by the grain size of the ferromagnetic particles in a simple and flexible way.     

Fabrication and performance of La0.8Sr0.2MnO3/YSZ graded composite cathodes for SOFC

The performance of multi-layer (1 − x) La_0.8Sr_0.2MnO₃/x YSZ graded composite cathodes was studied as electrode materials for intermediate solid oxide fuel cells (SOFC). The thermal expansion coefficient, electrical conductivity, and electrochemical performance of multi-layer composite cathodes were investigated. The thermal expansion coefficient and electrical conductivity decreased with the increase in YSZ content. The (1 -x)La_0.8Sr_0.2MnO₃/x YSZ composite cathode greatly increased the length of the active triple phase boundary line (TPBL) among electrode, electrolyte, and gas phase, leading to a decrease in polarization resistance and an increase in polarization current density. The polarization current density of the triple-layer graded composite cathode (0.77 A/cm²) was the highest and that of the monolayer cathode (0.13 A/cm²) was the lowest. The polarization resistance (R_p) of the triple-layer graded composite cathode was only 0.182 ω·cm² and that of the monolayer composite cathode was 0.323 ω·cm². The power density of the triple-layer graded composite cathode was the highest and that of the monolayer composite cathode was the lowest. The triple-layer graded composite cathode had superior performance.     

Height-related magnetoelectric performance of PZT/Ni layered composites

The effect of height on performance of the PZT/Ni cylindrical bilayered magnetoelectric(ME) composites was studied in situ in this paper.Multiple resonant peaks appear between 1 and 300 kHz frequency for cylinders of different heights.The first resonance frequency does not change with the cylinder height decreasing,but the second and the third resonant frequencies increase.The first three resonant modes are attributed to the cylinder radial,first-order height resonance,and second-order height resonance,respectively.The appropriate size and resonance frequency were chosen to obtain the highest ME voltage coefficient when designing cylindrical bilayered magnetoelectric devices.This article provides reference to design cylindrical magnetoelectric devices.     

Microstructure, spallation and corrosion of plasma sprayed Al2O3–13%TiO2 coatings

The electrochemical corrosion behaviours of the steel substrates coated with three different plasma sprayed Al₂O₃–13%TiO₂ coatings were studied in this paper. The three kinds of Al₂O₃–13%TiO₂ coatings were conventional ME coating, nanostructured NP coating and NS coating. There were micro cracks, laminar splats and straight columnar grains in ME coating. For the two nanostructured coatings, the laminar microstructure and columnar grains were not obvious. The NP coating had the highest hardness and spallation resistance. Electrochemical corrosion behaviour of the three coatings was mainly investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in aqueous Na₂SO₄ solution.     

Influence of temperature and illumination on the characteristics of nanocrystalline Ga0.29 Al0.71As based heterojunction prepared by MOCVD

The heterojunction between nanocrystalline n-Ga_0.29 Al_0.71As and p-GaAs was fabricated by using metal organic chemical vapor deposition, MOCVD. The elemental composition of the prepared film was confirmed by energy dispersive X-ray (EDX) spectroscopy. The morphology and crystal structure of the film were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. This work explores the electrical properties of nanocrystalline n-Ga_0.29 Al_0.71As/p-GaAs heterojunction (HJ) in the temperature range 300-400 K. The n-Ga_0.29 Al_0.71As/p-GaAs heterojunction exhibits high rectifying behavior with a low saturation current density. While increasing temperature, the saturation current of the junction is increased and however, its series resistance decreased. At all temperatures the junction exhibited three types of transport mechanisms namely recombination, diffusion-limited thermionic emission, and space-charge-limited current mechanism, respectively depending on the applied bias-voltage. While increasing temperature, the diffusion potential of the barrier decreased linearly and the temperature sensitivity coefficient of the junction is found to be 5.3 mV/K. The C-V characteristics were measured at different testing signal frequencies. Their frequency dependence is related to the influence of a HJ series resistance on these characteristics. The plot of 1/C² vs. the applied bias voltage behavior is linear, indicating the presence of abrupt junction. The effect of temperature and illumination on capacitance-voltage (C-V) characteristics of n-Ga_0.29 Al_0.71As/p-GaAs heterojunction was investigated. The J-V characteristics of n-Ga_0.29 Al_0.71As/p-GaAs heterojunction device were studied under illumination of 100 mW/cm² at different temperature in the range 300-400 K. It can be observed that the open circuit voltage, V_oc decrease continuously with increase in temperature, while J_sc increases with increase in temperature. The temperature coefficient dV_oc/dT and dJ_sc/dT were obtained. The photovoltaic parameters are also studied under effect of different illumination intensities.     

Tribological behavior of self lubricating Cu/MoS2 composites fabricated by powder metallurgy

The effects of MoS₂ content on microstructure, density, hardness and wear resistance of pure copper were studied. Copper-based composites containing 0–10% (mass fraction) MoS₂ particles were fabricated by mechanical milling and hot pressing from pure copper and MoS₂ powders. Wear resistance was evaluated in dry sliding condition using a pin on disk configuration at a constant sliding speed of 0.2 m/s. Hardness measurements showed a critical MoS₂ content of 2.5% at which a hardness peak was attained. Regardless of the applied normal load, the lowest coefficient of friction and wear loss were attained for Cu/2.5MoS₂ composite. While coefficient of friction decreased when the applied normal load was raised from 1 to 4 N at any reinforcement content, the wear volume increased with increasing normal load. SEM micrographs from the worn surfaces and debris revealed that the wear mechanism was changed from mainly adhesion in pure copper to a combination of abrasion and delamination in Cu/MoS₂ composites.     

Reciprocating wear behavior of 7075Al/SiC in comparison with 6061Al/Al2O3 composites

In the present study, the reciprocating wear behavior of 7075Al/SiC composites and 6061Al/Al₂O₃ composites that are prepared through liquid metallurgy route is analyzed to find out the effects of weight percentage of reinforcement and load at the fixed number of strokes on a reciprocating wear testing machine. The Metal Matrix Composite (MMC) pins are prepared with different weight percentages (10, 15 and 20%) of SiC and Al₂O₃ particles with size of 36 μm. Hardness of these composites increases with increase in wt.% of reinforcement. However, the impact strength decreases with increase in reinforcement content. The experimental result shows that the volume loss of MMC specimens is less than that of the matrix alloy. However, the volume loss is greater in 6061Al/Al₂O₃ composites when compared to 7075Al/SiC composites. The temperature rise near the contact surface of the MMC specimens increases with increase in wt.% of reinforcement and applied load. The coefficient of friction decreases with increase in load in both cases.     

微波原位制备作为锂离子电池电极材料的石墨烯/TiO2 纳米复合物

通过改造的家用微波炉,实现了原位高效制备石墨烯/TiO₂纳米复合物。结果表明：微波辅助法能够在商用锐钛矿型TiO₂纳米颗粒表面均匀制备石墨烯纳米片,通过SiO₂/Si的剧烈电晕放电,其制备时间仅需数分钟（最短3 min）。石墨烯纳米片的尺寸大约为50 nm且缺陷很少。TiO₂晶体结构仍为锐钛矿型,主要归功于极短的制备周期和较低的反应温度（600~700 ℃）。石墨烯具有优异的电导率,可以提升锂离子扩散速率、提高电子传输速率并降低接触电阻。在1 C（170 mA·g^-1）条件下石墨烯/TiO₂纳米复合物的电池放电比容量提高了2倍。与商业化锐钛矿型TiO₂纳米颗粒相比,在1 C到5 C的不同充放电倍率下,石墨烯/TiO₂纳米复合物的比容量差距显著扩大。     

Impedance analysis of thermally modified SrBi2(Nb0.5Ta0.5)2O9 ceramics

Aurivillius SrBi₂(Nb_0.5Ta_0.5)₂O₉ (SBNT 50/50) ceramics were prepared using the conventional solid-state reaction method. The obtained samples were thermally modified in high vacuum to study the influence of the formed defects on the dielectric and electrical properties of the samples. Scanning electron microscopy with an energy dispersion X-ray spectrometer was applied to investigate the grain structure and stoichiometry of the studied ceramics. Their dielectric properties were determined by impedance spectroscopy measurements. A strong low frequency dielectric dispersion was found to exist in this material which was controlled by thermal modification of the tested ceramics. This phenomenon can be ascribed to the presence of ionized space charge carriers such as oxygen and bismuth vacancies. The dielectric relaxation was defined on the basis of an equivalent circuit. Moreover the temperature dependence of various electrical properties was determined and discussed.     

Corrosion and Interdiffusion in a Ni/Fe–Cr–Al Couple Used for the Anode Side of Multi-Layered Interconnector for SOFC Applications

Under operating conditions in solid-oxide fuel cells (SOFC), metallic-interconnect plates form oxide scales (e.g., Cr₂O₃, Al₂O₃) on their surface, which have an electrically insulating effect and increase the contact resistance between the interconnect and the electrodes. In order to ensure high electrical conductivity between the electrodes and the interconnects, the formation of oxide scales on the interconnect surface must be prevented or minimized. The present work shows possibilities for improved contacts at the anodic side in solid-oxide fuel cells by plating an Fe–Cr–5.7Al interconnect with a Ni foil. Contact-resistance measurements and microscopic studies show the electrical behavior and corrosion of materials used at 800°C under an Ar/4 vol.% H₂/3 vol.% H₂O atmosphere. The results reveal that the interconnects coated with nickel exhibit low aging rates in the investigations performed and are thus suitable for use on the anode side.     

A study on the wear resistance of ZrO2/Al2O3 ceramic scissors for spinning and weaving

A new kind of zirconia matrix ceramic material (ZrO₂/Al₂O₃) has been developed with 3Y-PSZ (3 mol% Y₂O₃ partially stabilized ZrO₂) and the additive of alumina. The wear resistance of ZYA20 (3Y-PSZ+20 wt.% Al₂O₃) has been experimentally investigated compared with ZYA30 (3Y-PSZ+30 wt.% Al₂O₃) by the wear ring-block test. It is shown that the friction coefficients of ZYA20 and ZYA30 decrease with the increment of the applied load and the wear ratios increase with the increment of the applied load. It is also found that their wear mechanisms are plastic deformation, adhesive and abrasive wear, as well as stripping. The wear resistance of ZYA20 and ZYA30 are very good at low load and ZYA20 is stronger than ZYA30.     

Investigation on the Electrical Properties of Vacuum Cold Sprayed SiC-MoSi2 Coatings at Elevated Temperatures

SiC-MoSi₂ composite powders was prepared by wet milling with MoSi₂ powders and SiC loose grinding ball in alcohol solution. Vacuum cold spray (VCS) process was used to deposit SiC-MoSi₂ electric conducting composite coatings. The microstructure of the VCS SiC-MoSi₂ composite coatings were characterized by scanning electron microscopy. The electrical resistance of the coatings was measured using a four-point probe method. The effects of the deposition parameters on the electrical resistivity of the composite coatings were investigated. The electrical properties of the coatings at elevated temperatures in air and Ar gas atmospheres were also explored. The results show that the electrical resistivity of SiC-MoSi₂ coatings decreases with increasing He gas flow rates ranged from 3 to 6 L/min. The electrical resistivity increases with the increase in heat treatment temperature due to “pesting” behavior of MoSi_2. The electric conductive property of the VCS SiC-MoSi₂ coating is significantly improved after heat treatment at 1000 °C for 3 h in Ar protective atmosphere without oxidation. A minimum resistivity of the heat treated coating is 0.16 Ω · cm.     

C/C复合材料大气等离子喷涂mullite/ZrB2-MoSi2涂层抗烧蚀性能

采用大气等离子喷涂技术(APS)在C/C复合材料表面制备了mullite/ZrB₂-MoSi₂双层抗烧蚀涂层。借助XRD、SEM、EDS等分析手段对涂层的组织结构进行研究;基于氧丙烯焰烧蚀试验考察ZrB₂-MoSi₂/mullite复合涂层对C/C复合材料高温耐烧蚀性能的影响。结果表明,在1700 °C和1800 °C的氧丙烯焰下烧蚀60 s,ZrB₂-MoSi₂/mullite涂层试样的质量烧蚀率分别为3.49×10_-3 g/s与3.77×10_-3 g/s。其与单层ZrB₂-MoSi₂涂层试样相比,ZrB₂-MoSi₂/mullite涂层试样展现了出色的抗烧蚀性能。烧蚀过程中形成的硅酸盐玻璃可以作为热障层而减少氧气的进一步渗透,并且还具有自我封填缺陷的能力,使ZrB₂-MoSi₂/mullite涂层表现较好的抗烧蚀性。     

1/f noise in polyaniline/polyurethane (PANI/PU) blends

We have investigated the electrical conductivity and the low-frequency noise of spin coated polyaniline/polyurethane (PANI/PU) films on different substrates (free, on ceramic, PVC and Teflon) and different compositions. The layer thickness is between 12 and 220 μm. The range in conductivity at room temperature is from 10² to 10⁴ S/m and the sheet resistance is between 4 and 50 Ω. The fluctuations in the conductivity have a 1/f spectrum. The 1/f noise normalized for bias, frequency and unit area, C_us is proportional with the sheet resistance, R_sh.Our proposed model explains the proportionality C_us ∝ R_sh and the high value of the proportionality factor between C_us and R_sh. The typical elongated shape of the PANI component with a relative low number of noisy contacts between touching conducting elongated chains explains the strong noise in such materials.     

Impedance spectroscopy and dielectric properties of Ce and La substituted Pb0.7Sr0.3(Fe0.012Ti0.988)O3 nanoparticles

We present the structural, microstructural, dielectric and impedance behavior of Pb_0.7Sr_0.3[(Fe_2/3Ce_1/3)_0.012Ti_0.988]O₃ (PSFCT) and Pb_0.7Sr_0.3[(Fe_2/3La_1/3)_0.012Ti_0.988]O₃ (PSFLT) nanoparticles. These nanoparticles were prepared by a chemical synthesis route using polyvinyl alcohol as surfactant. The X-ray diffraction pattern shows polycrystalline nature with coexistence of tetragonal and cubic phase in both PSFCT and PSFLT nanoparticles. The average particle size has been measured using Scherer's relation. The average particle sizes also measured by TEM are 10 and 11 nm, and by SEM 9 and 12 nm, respectively, of PSFCT and PSFLT nanoparticles. By measuring the value of relative permittivity (?′) and loss (tan δ) at lower frequency, the dielectric properties show Maxwell-Wagner type interfacial polarization. However, due to nano size effect of PSFCT and PSFLT, dispersionless dielectric response has been observed up to higher frequency of 15 MHz. The frequency dependent real (Z′) and imaginary (Z″) parts of impedance confirmed the variation which was observed in dielectric properties. The values of resistance of grain boundaries, R_gb is higher than grains, R_g indicates that the effect of grain boundaries is dominant on electrical properties when the size of nanoparticles is quite small.