The synthesis and characterization of electrical and magnetic nanocomposite: PEDOT/PSS–Fe3O4

The poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate)–Fe₃O₄ (PEDOT/PSS–Fe₃O₄) nanoparticles have been prepared by using polystyrene sulfonic sodium (NaPSS) as a dispersant and dopant. The characterization of nanocomposites was investigated by transmission electron microscope, X-ray diffraction, UV spectroscopy, electrochemical study, four-probe, thermogravimetric analysis and magnetic property measurement system. XRD revealed the presence of spinel phase of Fe₃O₄ and the average size was calculated to be about 12 nm. The conductivity of nanocomposites at room temperature is excellent and it depends on the Fe₃O₄ content. The thermal stability of composites is outstanding. Higher saturation magnetization of 6.47 emu g⁻¹ (20 wt.% Fe₃O₄) was observed at 300 K.     

Synthesis,structure and electrical studies of praseodymium doped barium zirconium titanate

Praseodymium (Pr) doped barium zirconium titanate with nominal composition (Ba_1−xPr_x)(Zr_0.52Ti_0.48)O₃ (x = 0.1 and 0.2) were synthesized using solid state reaction method. X-ray analysis conform the formation of cubic phase Pr-doped barium zirconium titanate along with minor pyrochloric phase. The increase in grain size after primary investigation reveals the influence of Pr ions on the domain structure and its microstructure. In order to correlate the effect of the chemical composition with the conduction mechanism, different AC electrical parameters have been addressed. The frequency dependant tangent loss of the sample was less for both the ceramics. The temperature dependence results show that the dielectric parameters and resistivity increases as Pr-content in the ceramic increases; this is attributed to the grain size and dipole dynamics. Complex impedance (Z*) plots show frequency dependent behavior as the response for the grain resistance mechanisms. This mechanism has been represented by an equivalent circuit. The temperature dependence of the electrical conductivity and Seebeck coefficient showed n-type non-degenerated semiconductor in the measured temperature range. The temperature dependent conductivity measurement suggests a novel negative temperature coefficient of resistance behavior of the samples. Furthermore, the frequency dependent conductivity plot shows increasing behavior.     

短切炭纤维-炭复合材料的制备及传导性能和微观结构的研究

以中间相沥青基短切炭纤维和中间相沥青为原料,采用模压成型、炭化、致密化、高温石墨化等一系列常规工艺,制备了传导性能良好的炭/炭复合材料.主要考察了中间相沥青与中间相沥青基炭纤维质量配比对材料密度及传导性能的影响,并进一步研究了材料微晶参数的变化与材料性能的相关性.结果表明中间相沥青与纤维质量配比对材料的导热、导电性能以及微晶参数有很大影响.随着中间相沥青用量的增大,材料导热、导电性能均提高,石墨层间距d002减小,石墨微晶尺寸La、Lc增大;当中间相沥青与炭纤维质量比为 0.8时,制备出的炭/炭复合材料石墨微晶尺寸最大,常温传导性能最佳(垂直于压制方向的面向热导率为385W/(m·K),电阻率为2.85μΩ·m);进一步提高中间相沥青用量,石墨微晶尺寸La、Lc减小,材料的传导性能降低.     

Improved filling rate and enhanced magnetic properties of Fe-filled carbon nanotubes by annealing and magnetic separation

The filling rate of Fe nanowires in carbon nanotubes (CNTs) was improved by a post-treatment which involved annealing and magnetic separation. The annealing process transformed γ-Fe to ferromagnetic α-Fe, resulting in α-Fe-filled CNTs with improved magnetic properties. The Fe-filled CNTs were then separated from those unfilled CNTs due to the different attractive forces under magnetic field. Thermal gravimetric analysis (TGA) revealed that the purity of CNTs was improved after magnetic separation and the filling rate can be up to 40.0 wt.%, which is increased about 8.1% comparing with annealed CNTs. The saturation magnetization of CNTs reached 31.45 emu/g after magnetic separation.     

Fe3O4纳米粒子修饰碳纳米管的制备及其磁学性能（英文）

通过FeCl2.4H2O和FeCl3.6H2O混合共沉淀,合成平均粒径为6 nm和10 nm的Fe3O4纳米粒子。然后将两种Fe3O4纳米粒子分别与经HNO3氧化处理的多壁碳纳米管(MWCNTs)置于乙醇水溶液(水和乙醇的体积比为1∶1)中,在超声波作用下制备Fe3O4/MWCNT复合材料。用高分辨透射电子显微镜、X-射线光电子能谱、振动样品磁强计、X射线衍射仪、热重分析仪对所制备的Fe3O4/MWCNT复合材料进行表征。结果表明:由6 nm和10 nm Fe3O4纳米粒子所制备的Fe3O4/MWCNT复合材料中,Fe3O4的质量分数分别为26.65%和29.3%,相应的磁饱和强度分别为16.5 emug-1和7.5 emug-1。     

Extraordinary role of Ce–Ni elements on the electrical and magnetic properties of Sr–Ba M-type hexaferrites

The structural, electrical and magnetic behavior of Sr_0.5Ba_0.5−xCe_xFe_12−yNi_yO₁₉ (where x = 0.00–0.10; y = 0.00–1.00) hexaferrite nanomaterials are reported in this paper. The structural analysis indicates that the Ce–Ni doped Sr–Ba M-type hexaferrite samples synthesized by the co-precipitation method are stoichiometric, single magnetoplumbite phase with crystallite sizes in the range of 35–48 nm. The dc-electrical resistivity of the pure Sr–Ba hexaferrite is enhanced to almost 10² times by doping with Ce–Ni contents of x = 0.06; y = 0.60. The dielectric constant and dielectric loss tangent decrease to values 14 and <0.2, respectively, by increasing the frequency up to 1 MHz. Small relaxation peaks at frequencies >10⁵ Hz are observed for the samples with Ce content of x > 0.06. The values of saturation magnetization increase from 66.32 to 84.33 emu/g and remanance magnetization from 42.64 to 56.01 emu/g but coercivity decreases from 2.85 to 1.59 kOe by substitution of Ce–Ni. Sharp ferri-paramagnetic transition is observed in the samples, which is confirmed by DSC results. Ce–Ni substitution acts to reduce the electron-hopping between Fe²⁺/Fe³⁺ ions and also improves the magnetic properties. These characteristics are desirable for their possible use in microwave and chip devices.     

流化床CVD法制备单壁碳纳米管:反应温度与时间的影响

基于负载法Fe—MgO体系催化剂研究了化学气相沉积（CVD）法在流化床反应器中反应温度和时间对单壁碳纳米管（SWCNTs）生长的影响。通过气相色谱对尾气进行实时在线分析，获得了CH4在反应过程中的转化率随时间的变化规律。并对不同反应温度和反应时间所获产品进行了TEM、Raman和TGA等表征。结果表明，900℃是最佳的反应温度，反应温度过低会降低催化剂活性，反应温度过高则容易使催化剂过快失活。在合适的反应温度下，反应前10min催化剂的平均活性较高，能够得到较高质量的SWCNTs，10min后催化剂基本失活。     

Mössbauer and magnetic studies of Mg1+2xSbxFe2−3xO4 spinel ferrites

Spinel-related Mg_1+2xSb_xFe_2−3xO₄ samples (x = 0.0, 0.05, 0.10, 0.15, 0.20, and 0.30) prepared using the conventional double sintering technique were investigated using ⁵⁷Fe Mössbauer spectroscopy and magnetic measurements. Mössbauer spectra favor a cationic distribution of the form (Mg_δFe_1−δ)^A[Mg_1+2x−δSb_xFe_1+δ−3x]^BO₄ among the tetrahedral-A and octahedral-B sites of the spinel structure. The cation distribution parameter (δ) was found to vary with the Sb⁵⁺ concentration (x). The Mössbauer hyperfine magnetic fields at both sites and the Curie temperatures of the ferrites decrease as x increases. This was attributed to gradual weakening in the magnetic exchange interaction as more Fe³⁺ ions are substituted by diamagnetic Sb⁵⁺ and Mg²⁺ ones. The sample with x = 0.30 exhibits short range magnetic order due to cationic clustering and/or superparamagnetism. The magnetization of all samples was found to be temperature-dependent implying that δ depends on temperature in addition to x. At low temperatures the substituted ferrites (x ≠ 0.0) unexpectedly exhibit higher magnetization values relative to that of the pure ferrite MgFe₂O₄. This behavior, while at variance with the Néel's model for ferrimagnetism, is explicable in terms of the spin canting mechanism proposed in the Yafet–Kittel model.     

Synthesis, characterization and electrical conductivity studies on A3Bi2P3O12 (A = Na, K) materials

Crystalline Na₃Bi₂P₃O₁₂, K₃Bi₂P₃O₁₂ and glassy K₃Bi₂P₃O₁₂ compounds were prepared by solid-state reaction method. The prepared samples are characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry. The crystalline materials are found to be orthorhombic. The electrical conductivity measurements on the crystalline and glassy samples show that at ∼373 K, the σ_DC for crystalline K₃Bi₂P₃O₁₂ (0.81 × 10⁻⁸ S/cm) is about two orders of magnitude higher than the corresponding glassy phase (1.25 × 10⁻¹⁰ S/cm). The scaling results show that the conductivity relaxation mechanism is independent of temperature.     

A study of the influence of crystallite size on the electrical and magnetic properties of CuFe2O4

An attempt has been made to clarify the fundamental assumption that the properties of materials change as the crystallite size of the material is reduced below 100 nm. CuFe₂O₄ samples of different crystallite sizes were prepared by the sol–gel and combustion methods and then analyzed by X-ray diffraction (XRD), thermal analyses (TGA/DTG) and scanning electron microscopy (SEM) techniques. The magnetic properties were studied by measuring the AC magnetic susceptibility (χ) and the Mössbauer spectroscopy. The DC electrical resistivity, dielectric constant, dielectric loss tangent, Curie temperature and hyperfine splitting of the samples change with the crystallite size. The change in the electrical properties is attributed to the formation of discrete energy levels instead of the bands. However, the magnetic parameters change due to the existence of non magnetic surface layers. The isomer shift and the hyperfine splitting show gradual increase with the increase in crystallite sizes.     

Preparation and characterization of (V1−xAlx)2O3 ultrafine powders by chemical doping method

(V_1−xAl_x)₂O₃ ultrafine powders have been synthesized successfully by pyrolysizing poly-crystalline Al-doped precursor, Al-doped (NH₄)₅[(VO)₆(CO₃)₄(OH)₉]·10H₂O in H₂ atmosphere at 1373 K for the first time. The relation between the ratio of Al/V in the VOCl₂ solution and that in polycrystalline Al-doped precursor was studied. The result shows that this chemical doping method is successful, and the Al (III) content in precursor is controllable. The lattice parameters of (V_1−xAl_x)₂O₃ determined by XRD at room temperature and high-temperature reveal that the Al (III) enter the V₂O₃ lattice. The SEM micrograph shows that the size of the powder particles is about 100-200 nm. The DSC and magnetic susceptibility results of the (V_1−xAl_x)₂O₃ demonstrate that the powders exhibit the intrinsic phase transition properties.     

Mössbauer and magnetic study of Mn, Zr and Cd substituted W-type hexaferrites prepared by co-precipitation

BaCo_2−xMn_xFe_16−2y(Zr–Cd)_yO₂₇ (x = 0–0.5 and y = 0–1.0) hexaferrite nanocrystallites of average sizes in the range of 33–42 nm are synthesized by the chemical co-precipitation method. The synthesized materials are characterized using different techniques including X-ray diffraction (XRD), energy dispersive X-ray florescence (ED-XRF), scanning electron microscope (SEM), Mössbauer spectrometer and vibrating-sample magnetometer (VSM). Based on analysis of the data obtained from Mössbauer spectral studies, doping is believed to have occurred preferably in the vicinity of 12k sub-lattice, i.e. f_IV (4e, 4f_IV), 2b (6g, 4f) and 2d site. Variations in the saturation magnetization (77.1–60.9 emu g⁻¹), remanent magnetization (22.08–31.23 emu g⁻¹) and coercivity (1570.1–674.7 Oe) exhibit tunable behavior with dopant content and therefore can be useful for application in various magnetic devices.     

Effect of the Mn ion on electrical and magnetic properties of orthorhombic perovskite-type Ca(Mn1−xTix)O3−δ

Orthorhombic perovskite-type Ca(Mn_1−xTi_x)O_3−δ (0 ≤ x ≤ 0.7) was synthesized at 1173 K for 12 h in a flow of oxygen from a precursor gel prepared using citric acid and ethylene glycol. The Mn³⁺ ion was generated by substituting a Ti⁴⁺ ion in CaMnO₃. The average particle size was 100-300 nm and did not depend on x. The lattice constants and the (Mn, Ti)-O distance increased linearly with increasing x. The variation in global instability index (GII) indicated that the instability of the structure increases monotonically with increasing x. Ca(Mn_1−xTi_x)O_3−δ was an n-type semiconductor that had its minimum values of electrical resistivity (ρ) and activation energy (E_a) at x = 0.1. Ca(Mn_1−xTi_x)O_3−δ (x = 0 and 0.1) exhibited a weak ferromagnetic behavior. The variation in μ_eff indicated that the spin state of the Mn³⁺ ion changes from low to high at x = 0.1, then reverts to low in the range of 0.2 ≤ x ≤ 0.7. The variations in ρ and E_a are explained by the number of electrons according to the change in the spin state of the Mn³⁺ ion.     

Effect of lattice matching on microstructure and electrical conductivity of epitaxial ARuO3 (A = Sr, Ca and Ba) thin films prepared on (001) LaAlO3 substrates by laser ablation

(001) SrRuO₃ (SRO), (001) CaRuO₃ (CRO) and (205) BaRuO₃ (BRO) thin films were epitaxially grown on (001) LaAlO₃ substrates by laser ablation, and the effect of lattice matching on the microstructure and electrical conductivity was investigated. (001) SRO and (001) CRO thin films had a terrace with orthogonal step structure, whereas (205) BRO thin film had an orthogonal structure with tetragonal grains. Epitaxial thin films showed metallic conduction, and the (001) CRO thin films exhibited the highest electrical conductivity, i.e. 1.5 × 10⁵ S m^− 1, among the (001) SRO, (001) CRO and (205) BRO thin films. The smaller misfit between thin film and substrate could be associated with the higher electrical conductivity.