Synthesis of nanocrystalline Zn0.5Mn0.5Fe2O4 via in situ polymerization technique

Nanocrystalline Zn_0.5Mn_0.5Fe₂O₄ was synthesized through the pyrolysis of polyacrylate salt precursors prepared via in situ polymerization of the metal salts and acrylic acid. The pyrolysis behavior of the polymeric precursors was studied by use of thermal analysis. The as-obtained product was characterized by powder X-ray diffraction (XRD), transmission electron microscope (TEM), electron diffraction (ED) pattern, scanning electron microscopy (SEM) and electron dispersive X-ray (EDX) analysis. The results revealed that the particle size is in the range of 15–25 nm for Zn-Mn ferrites with good crystallinity. Magnetic properties of the sample at 300 K were measured using a vibrating sample magnetometer, which showed that the sample exhibited characteristics of superparamagnetism.     

针状纳米MnxNi0.5-xZn0.5Fe2O4的共沉淀法制备及表征

通过在碱液中共沉淀Mn²⁺、Ni²⁺和Fe²⁺后制备了棒状的前躯体,前躯体于不同温度煅烧后制得了Mn_xNi_0:5-xZn_0:5Fe₂O₄棒状体. 利用X射线衍射仪和透射电镜对棒状体的物相、形貌及粒径进行了表征,并利用振动样品磁强计对磁性能进行研究. 结果表明长径比大于15的棒状,随着x值的增加,Mn_xNi_0:5-xZn_0:5Fe₂O₄样品的直径增加,长度下降,长径比变小,当x=0.5时其直径在50 nm左右而长径比减小到7～8. 随着x值的增加,样品的矫顽力先增加后减少,x值达到0.4时样品的矫顽力再次增加,当煅烧温度为600 oC,x=0.5时样品的矫顽力最大为134.3 Oe. 饱和磁化强度随着x值的增加先增加后减少,当煅烧温度为800 oC和x=0.2时达到最大为68.5 Oe.     

Preparation and magnetic properties of BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite

Nanocomposite of hard (BaFe₁₂O₁₉)/soft ferrite (Ni_0.8Zn_0.2Fe₂O₄) have been prepared by the sol–gel process. The nanocomposite ferrite are formed when the calcining temperature is above 800 °C. It is found that the magnetic properties strongly depend on the presintering treatment and calcining temperature. The “bee waist” type hysteresis loops for samples disappear when the presintering temperature is 400 °C and the calcination temperature reaches 1100 °C owing to the exchange-coupling interaction. The remanence of BaFe₁₂O₁₉/Ni_0.8Zn_0.2Fe₂O₄ nanocomposite ferrite with the mass ratio of 5:1 is higher than a single phase ferrite. The specific saturation magnetization, remanence magnetization and coercivity are 63 emu/g, 36 emu/g and 2750 G, respectively. The exchange-coupling interaction in the BaFe₁₂O₁₉/Ni_0.8Zn_0.2Fe₂O₄ nanocomposite ferrite is discussed.     

聚对苯撑/LiNi0.5Fe2O4纳米复合热电材料的制备及其性能研究

本文以流变相反应法原位合成了聚对苯撑/LiNi_0.5Fe₂O₄纳米复合热电材料,并对其热电性能进行表征,研究了放电等离子烧结时保温时间对其热电性能的影响.结果发现,复合材料铁氧体颗粒粒径为100---300nm,其外部被一层聚对苯撑膜包覆.电子在Fe²⁺和Fe³⁺之间的跳跃机理在铁氧体电导中占主导作用,因此聚对苯撑/LiNi_0.5Fe₂O₄复合材料具有n型导电特性.随着保温时间增加,复合材料电导率基本不变,但热导率逐渐增大且Seebeck系数逐渐减小,导致热电优值系数降低.由于结合了有机物高电导率和低热导率以及无机材料高赛贝克系数的优点,所制备的复合材料热电性能较单一材料有较大提高.     

Effect of sintering temperature and the particle size on the structural and magnetic properties of nanocrystalline Li0.5Fe2.5O4

Sintering temperature and particle size dependent structural and magnetic properties of lithium ferrite (Li_0.5Fe_2.5O₄) were synthesized and sintered at four different temperatures ranging from 875 to 1475 K in the step of 200 K. The sample sintered at 875 K was also treated for four different sintering times ranging from 4 to 16 h. Samples sintered at 1475 K have the cubic spinel structure with a small amount of α-Fe₂O₃ (hematite) and γ-Fe₂O₃ (maghemite). The samples sintered at≤1275 K do not show hematite and maghemite phases and the crystals form the single phase spinel structure with the cation ordering on octahedral sites. Particle size of lithium ferrite is in the range of 13-45 nm, and is depend on the sintering temperature and sintering time. The saturation magnetization increased from 45 to 76 emu/g and coercivity decreases from 151 to 139 Oe with an increase in particle size. Magnetization temperature curve recorded in ZFC and FC modes in an external magnetic field of 100 Oe. Typical blocking effects are observed below about 244 K. The dielectric constant increases with an increase in sintering temperature and particle size.     

Effect of grain size on the magnetic properties of superparamagnetic Ni0.5Zn0.5Fe2O4 nanoparticles by co-precipitation process

Ni_0.5Zn_0.5Fe₂O₄ (NZFO) spinel-type nanoparticles were directly fabricated by the chemical co-precipitation process using metal nitrate and acetate as precursors since nitrogen and carbon would be taken away in the forms of oxynitride and oxycarbide, respectively, after the precursors were annealed and then investigated in detail by employing X-ray diffraction (XRD), magnetic measurement and Raman spectroscopy. XRD analysis indicates that the as-prepared nanocrystals are all of a pure cubic spinel structure with their sizes ranging from 20.8 to 53.3 nm, as well as peaks of some samples shifting to lower angles due to lattice expansion. Calculations from the derived XRD data indicate that the activation energy is 30.83 kJ/mol. The magnetic measurements show that these samples are superparamagnetic. The saturation magnetization increases with annealing temperature, which may be explained by super-exchange interactions of Fe ions occurring at A- and B-sites. The variation of coercivity with particle size is interpreted on the basis of domain structure and crystal anisotropy. Furthermore, these nanoparticles exhibit a redshift phenomenon at lower temperatures seen in the Raman spectra, which could be related to ionic substitution.     

NbTi0.5Ni0.5O4 as anode compound material for SOFCs

NbTi_0.5Ni_0.5O₄ (NTNO) has been prepared using solid state synthesis and investigated as a potential anode material. The oxide form of NTNO has single phase rutile-type structure with tetragonal (P42/mnm) space group. The reduced form is a composite of nano-scaled particles of metallic Ni and Nb_1.33Ti_0.67O₄ phase. Reduced NTNO showed high electronic conductivity up to 280 S.cm^− 1 at 900 °C in reducing atmosphere, but suffers from low CTE equal to 3.78 10^− 6 K^− 1. Studies of NTNO as anode material were carried out in a three electrode - electrochemical half cell configuration under pure humidified H₂ at 900 °C using a 2 mm thick zirconia electrolyte and without any additional current collector material. The results show a reasonable series resistance (R_s) equal to 2.7 Ωcm² (about 50% higher than for metallic gold layers) indicating a good current collection performance for a 10 μm layer of material. The polarization resistance (R_p) was equal to 33 Ωcm² and is attributed to a poor density of three phase boundaries (TPB) and shortage of oxide ion conduction in the anode layer. The results show the potential of NTNO as an anode material, especially after optimization of the microstructure towards the increase of TPB length.     

低维Bi2Fe4O9晶体的控制生长及其光催化性能研究

Low-dimensional Bi₂Fe₄O₉ nanosheets and microrods have been selectively prepared by a solvothermal method, from which the growth of the Bi₂Fe₄O₉ crystals can be controlled by the variation of reaction conditions. Structure determination showed that the nanosheets are mainly exposed by {001} facets while the microrods are exposed by {110} facets. Ab- sorption spectra revealed that there are two bandgaps observed for both nanosheets (at 1.9 and 1.55 eV) and microrods (1.7 and 1.45 eV), and they both would be available for the sunlight photocatalysis e ciently due to the intensive absorption ability in a wide region. Photocatalytic investigation demonstrated that the overall photocatalytic performance of the microrods is prior to that of the nanosheets due to the variation of bandgaps and exposed facets. The present report provides a useful alternative strategy for the controlling growth of nanostructures and/or microcrystals besides the present demonstration of the Bi₂Fe₄O₉ crystals with diflerent bandgaps and facets that would be able to tune the corresponding photocatalytic ability selectively.     

Dielectric properties and relaxation behavior of [TMA]2Zn0.5Cu0.5Cl4 compound

The [TMA]₂Zn_0.5Cu_0.5Cl₄ hybrid material was prepared and its dielectric spectra were measured in the 10⁻¹ Hz-10⁶ Hz frequency range and 200-305 K temperature interval. The dielectric permittivity showed a ferroelectric-paraelectric phase transition at 293 K. Double relaxation peaks are observed in the imaginary part of the electrical modulus, suggesting the presence of grain and grain boundary in the sample. The frequency dependent conductivity was interpreted in term of Jonscher's law: σ(ω)=σ_dc+Aωⁿ. The temperature dependent of the dc conductivity (σ_dc) was well described by the Arrhenius equation: σ_dcT=σ_o×exp(−E_a/kT).     

First-principle study of electronic structure and stability of Sn0.5Sb0.5O2

A theoretical study on Sb-doped SnO₂ has been carried out by means of periodic density functional theory (DFT) at generalized gradient approximation (GGA) level. Stability and conductivity analyses were performed based on the formation energy and electronic structures. The results show that Sn_0.5Sb_0.5O₂ solid solution is stable because the formation energy of Sn_0.5Sb_0.5O₂ is −0.06 eV. The calculated energy band structure and density of states showed that the band gap of SnO₂ narrowed due to the presence of the Sb impurity energy levels in the bottom of the conduction band, namely there is Sb 5s distribution of electronic states from the Fermi level to the bottom of conduction band after the doping of antimony. The studies provide a theoretical basis to the development and application of Sn_1−xSb_xO₂ solid solution electrode.     

Green synthesis and characterization of superparamagnetic Fe3O4 nanoparticles

In this paper, we have first demonstrated a facile and green synthetic approach for preparing superparamagnetic Fe₃O₄ nanoparticles using α-d-glucose as the reducing agent and gluconic acid (the oxidative product of glucose) as stabilizer and dispersant. The X-ray powder diffraction (XRD), X-ray photoelectron spectrometry (XPS), and selected area electron diffraction (SAED) results showed that the inverse spinel structure pure phase polycrystalline Fe₃O₄ was obtained. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results exhibited that Fe₃O₄ nanoparticles were roughly spherical shape and its average size was about 12.5 nm. The high-resolution TEM (HRTEM) result proved that the nanoparticles were structurally uniform with a lattice fringe spacing about 0.25 nm, which corresponded well with the values of 0.253 nm of the (3 1 1) lattice plane of the inverse spinel Fe₃O₄ obtained from the JCPDS database. The superconducting quantum interference device (SQUID) results revealed that the blocking temperature (T_b) was 190 K, and that the magnetic hysteresis loop at 300 K showed a saturation magnetization of 60.5 emu/g, and the absence of coercivity and remanence indicated that the as-synthesized Fe₃O₄ nanoparticles had superparamagnetic properties. Fourier transform infrared spectroscopy (FT-IR) spectrum displayed that the characteristic band of Fe-O at 569 cm⁻¹ was indicative of Fe₃O₄. This method might provide a new, mild, green, and economical concept for the synthesis of other nanomaterials.     

Electronic structure studies of the spinel CoFe2O4 by X-ray photoelectron spectroscopy

The spinel CoFe₂O₄ has been synthesized by combustion reaction technique. X-ray photoelectron spectroscopy shows that samples are near-stoichiometric, and that the specimen surface both in the powder and bulk sample is most typically represented by the formula (Co_0.4Fe_0.6)[Co_0.6Fe_1.4]O₄, where cations in parentheses occupy tetrahedral sites and those within square brackets in octahedral sites. The results demonstrate that most of the iron ions are trivalent, but some Fe²⁺ may be present in the powder sample. The Co 2p_3/2 peak in powder sample composed three peaks with relative intensity of 45%, 40% and 15%, attributes to Co²⁺ in octahedral sites, tetrahedral sites and Co³⁺ in octahedral sites. The O 1s spectrum of the bulk sample is composed of two peaks: the main lattice peak at 529.90 eV, and a component at 531.53 eV, which is believed to be intrinsic to the sample surface. However, the vanishing of the O 1s shoulder peak of the powder specimen shows significant signs of decomposition.     

The effect of Si surface nitridation on the interfacial structure and electrical properties of (La2O3)0.5(SiO2)0.5 high-k gate dielectric films

Thermal stability, interfacial structures and electrical properties of amorphous (La₂O₃)_0.5(SiO₂)_0.5 (LSO) films deposited by using pulsed laser deposition (PLD) on Si (1 0 0) and NH₃ nitrided Si (1 0 0) substrates were comparatively investigated. The LSO films keep the amorphous state up to a high annealing temperature of 900 °C. HRTEM observations and XPS analyses showed that the surface nitridation of silicon wafer using NH₃ can result in the formation of the passivation layer, which effectively suppresses the excessive growth of the interfacial layer between LSO film and silicon wafer after high-temperature annealing process. The Pt/LSO/nitrided Si capacitors annealed at high temperature exhibit smaller CET and EOT, a less flatband voltage shift, a negligible hysteresis loop, a smaller equivalent dielectric charge density, and a much lower gate leakage current density as compared with that of the Pt/LSO/Si capacitors without Si surface nitridation.     

Green synthesis of soya bean sprouts-mediated superparamagnetic Fe3O4 nanoparticles

Superparamagnetic Fe₃O₄ nanoparticles were first synthesized via soya bean sprouts (SBS) templates under ambient temperature and normal atmosphere. The reaction process was simple, eco-friendly, and convenient to handle. The morphology and crystalline phase of the nanoparticles were determined from scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD) spectra. The effect of SBS template on the formation of Fe₃O₄ nanoparticles was investigated using X-ray photoemission spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FT-IR). The results indicate that spherical Fe₃O₄ nanoparticles with an average diameter of 8 nm simultaneously formed on the epidermal surface and the interior stem wall of SBS. The SBS are responsible for size and morphology control during the whole formation of Fe₃O₄ nanoparticles. In addition, the superconducting quantum interference device (SQUID) results indicate the products are superparamagnetic at room temperature, with blocking temperature (T_B) of 150 K and saturation magnetization of 37.1 emu/g.     

Surface modification of LiMn2O4 thin films at elevated temperature

In order to improve the cycle stability of spinel LiMn₂O₄ electrode at elevated temperature, the LiCoO₂-coated and Co-doped LiMn₂O₄ film were prepared by an electrostatic spray deposition (ESD) technique. LiCoO₂-coated LiMn₂O₄ film shows excellent cycling stability at 55 °C compared to pristine and Co-doped LiMn₂O₄ films. The samples were studied by X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The excellent performance of LiCoO₂-coated LiMn₂O₄ film can be explained by suppression of Mn dissolution. On the other hand, the LiCoO₂-layer on the LiMn₂O₄ surface allows a homogenous Li⁺ insertion/extraction during electrochemical cycles and improves its structure stability.     

Preparation of LiNi0.5Mn0.5O2 cathode materials by urea hydrolysis coprecipitation

Layered LiNi_0.5Mn_0.5O₂ has been successfully synthesized via urea hydrolysis coprecipitation method. Well-crystallized LiNi_0.5Mn_0.5O₂ was obtained after calcinations of coprecipitation precursors and lithium salts at 450 °C for 3 h and following 900 °C for 10 h in air. Both the precursors and LiNi_0.5Mn_0.5O₂ powders show an agglomerated secondary structure with crystalline particles inside. The quasi-spherical morphology of the precursors was maintained during the calcinations. The first charge and discharge capacities of as-prepared LiNi_0.5Mn_0.5O₂ were 200 and 165mAh/g respectively. The discharge capacity of about 160mAh/g was retained after 10cycles for as-prepared samples.     

Electronic band structure and Fermi surface of new low-temperature Ni-based superconductors: 3.3 K (Ni2P2)(Sr4Sc2O6) and 2.7 K (Ni2As2)(Sr4Sc2O6) from first principles

Based on first-principle FLAPW-GGA calculations, we have investigated structural and electronic properties of the recently synthesized tetragonal (space group P4/nmm) nickel-based pnictide oxide superconductors: 3.3 K (Ni₂P₂)(Sr₄Sc₂O₆) and 2.7 K (Ni₂As₂)(Sr₄Sc₂O₆). Optimized structural data, electronic bands, total and partial densities of states, and Fermi surface topology have been obtained and discussed in comparison with available experiments and with their Fe-based (Fe₂P₂)(Sr₄Sc₂O₆) and (Fe₂As₂)(Sr₄Sc₂O₆) analogs.     

Immobilization of glucose oxidase using CoFe2O4/SiO2 nanoparticles as carrier

Aminated-CoFe₂O₄/SiO₂ magnetic nanoparticles (NPs) were prepared from primary silica particles using modified StÖber method. Glucose oxidase (GOD) was immobilized on CoFe₂O₄/SiO₂ NPs via cross-linking with glutaraldehyde (GA). The optimal immobilization condition was achieved with 1% (v/v) GA, cross-linking time of 3 h, solution pH of 7.0 and 0.4 mg GOD (in 3.0 mg carrier). The immobilized GOD showed maximal catalytic activity at pH 6.5 and 40 °C. After immobilization, the GOD exhibited improved thermal, storage and operation stability. The immobilized GOD still maintained 80% of its initial activity after the incubation at 50 °C for 25 min, whereas free enzyme had only 20% of initial activity after the same incubation. After kept at 4 °C for 28 days, the immobilized and free enzyme retained 87% and 40% of initial activity, respectively. The immobilized GOD maintained approximately 57% of initial activity after reused 7 times. The K_M (Michaelis-Menten constant) values for immobilized GOD and free GOD were 14.6 mM and 27.1 mM, respectively.     

A study of nano-sized surface coating on LiMn2O4 materials

The present study used the Pechini process with a heat treatment to synthesize LiMn₂O₄ powder (LMO). After surface coating, a nano-sized oxidative film of Li-Ni-Mn formed on the surface of the LMO-Ni powders. The concentration of Mn³⁺ for the LMO-Ni powder was lower and the average electrovalence of Mn exceeded the theoretical value, resulting in the initial capacity of the LMO-Ni powder being lower than the LMO powder. However, the LMO-Ni powder with the Li/Ni film not only restrained Mn ions from dissolving into the electrolyte, but also improved the charge-discharge cycling capacity.     

Mossbauer, Raman and X-ray diffraction studies of superparamagnetic NiFe2O4 nanoparticles prepared by sol-gel auto-combustion method

Superparamagnetic nickel ferrite single phase nanoparticles with the average crystallite size of ∼9 nm have been synthesized at a low temperature (220 °C) by the sol-gel auto-combustion method. In the present study the as prepared powder was further calcined at different temperatures for 4 h, resulting in nanoparticles of larger size. The nanoparticles exhibited superparamagnetic behavior and changes in cation distribution as revealed by the Mossbauer, Raman and X-ray diffraction studies. The Mossbauer spectra collected at 5 K and under 5 T applied magnetic field showed mixed spinel structure and canted spin order for the nanoparticles, whereas there is collinear spin order with inverse spinel structure for larger particles. The vibrational spectra of the nanoparticles showed a redshift and broadening in the Raman line shape due to confinement effects.