Effects of water on the properties of Fe3O4@C superparamagnetic nanospheres

ABSTRACT

Fe₃O₄@C nanospheres have potential applications in the field of magnetic separation, magnetic hyperthermia, magnetic targeting and magnetic resonance imaging (MRI). The carbon layers formed around Fe₃O₄ nanopaticles determined the adsorption properties of this material. In this study, Fe₃O₄@C was prepared by a simple one-pot solvothermal method, in which different amount of water was added to investigate the influences of water on the properties of Fe₃O₄@C nanospheres. The resulted samples were characterized by techniques of TEM, FT-IR, UV–Vis and BET, and found that the thickness of carbon layer, the intensity of surface carboxyl group and the adsorption characters were significantly changed by introducing additional water in autoclave.     

Preparation of Multi-walled Carbon Nanotube/Polyaniline/Fe3O4 Composites

A method to prepare multi-walled carbon nanotube/polyaniline/Fe₃O₄ nanocomposites was developed. Acid-treated multi-walled carbon nanotubes (MWCNTs) were first encapsulated with polyaniline (PANI) by an in-situ micro-emulsion polymerization and then reacted with Fe₃O₄ modified with aniline dimer (ADM-Fe₃O₄). Fourier transform infrared spectrometry demonstrated that there existed chemical linkages between the MWCNTs and the PANI as well as between the MWCNTs and the ADM-Fe₃O₄ nanoparticles. The morphology of the nanocomposites was examined using transmission electron microscopy. The bulk structure of the nanocomposites was investigated with X-ray diffraction. The resulting products could be separated from the deionized water under an external magnetic field within about several seconds.     

表面改性对超顺磁性Fe_3O_4纳米粒子性能的影响

采用超声波辅助部分还原共沉淀法制备超顺磁性Fe3O4纳米粒子。采用红外光谱仪(FT-IR)、X射线衍射(XRD)、振动样品磁强计(VSM)和粒径测试等手段对磁性纳米粒子进行表征,研究了不同表面改性剂(油酸、十二烷基苯磺酸钠、葡聚糖)对制备的磁性粒子的晶粒尺寸、磁性能及颗粒分散性的影响。结果表明,采用表面活性剂包覆改性后Fe3O4纳米粒子的XRD峰明显宽化,晶粒直径由未改性的18.5nm减小至6.0~9.0nm,饱和磁化强度因晶粒尺寸的减小而降低,且改性后颗粒在溶液中的分散性提高。     

Construction and electrochemical performances of the three-dimensional nano NiCo2O4

ABSTRACT

Bilayer NiCo₂O₄/NiCo₂O₄ nanosheet arrays on nickel foam (NF) are fabricated by a two-step solution-based method, which involves in hydrothermal process and chemical bath deposition. Compared with the monolayer NiCo₂O₄/NF electrode, the NiCo₂O₄/NiCo₂O₄/NF displays the unique micro-nanometer hierarchical and porours structure and has excellent pseudocapacitive behaviors in 6 M KOH, which exhibits high specific capacitances of 2363.64 F g^?1 at a constant current density of 0.5 Ag^?1, and 1454.55 F g^?1 at the higher current density of 8 Ag^?1, and shows a favourable cycling stability of 77.5% retention after 1000 cycles.     

Formation Mechanism of Plate-like Bi4Ti3O12 Particles in Molten Salt Fluxes

The plate-like Bi₄Ti₃O₁₂ particles were prepared by molten salt synthesis method. The influence of sintering temperature and cooling process on the microstructure of Bi₄Ti₃O₁₂ powders was studied. Much larger particles were formed at higher temperatures. The particles could grow larger in slow cooling process. The formation mechanism of plate-like Bi₄Ti₃O₁₂ particles in Na₂SO₄-K₂SO₄ system could be viewed as four processes: (1) solid reaction and nucleation, (2) plate-like structure formation, (3) diffusion and edge nucleation, (4) diffusion and epitaxial growth.     

Microwave dielectric properties of B2O3-added Li2MgTiO4 ceramics for LTCC applications

Li₂MgTiO₄ (LMT) ceramics which are synthesized using a conventional solid-state reaction route. The LMT ceramic sintered at 1250°C for 4 h had good microwave dielectric properties. However, this sintering temperature is too high to meet the requirement of low-temperature co-fired ceramics (LTCC). In this study, the effects of B₂O₃ additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B₂O₃ additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B₂O₃ sintered at 925°C for 4 h was found to exhibit optimum microwave dielectric properties: dielectric constant 15.16, quality factor 64,164 GHz, and temperature coefficient of resonant frequency -28.07 ppm/°C. Moreover, co-firing of the LMT ceramic with 8 wt% B₂O₃ and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B₂O₃ sintered at 925°C for 4 h is suitable for LTCC applications.     

Fatigue Melioration of Neodymium-Modified Bi4Ti3O12 Ceramics

Pure and Nd-modified Bi₄Ti₃O₁₂ ceramics were prepared using the conventional solid state reaction method and their dielectric properties and mechanical properties are investigated. It shows that the activation energy of oxygen vacancies is enhanced whereas the concentration of oxygen vacancies is reduced when Bi³⁺ ions are partially substituted by Nd³⁺ ions. The Cole-Cole fitting to the dielectric loss reveals a strong correlation among oxygen vacancies. The strong correlation reduces the activation energy of oxygen vacancies efficiently. Therefore, we conclude that the diluted oxygen vacancies concentration is the origin of the excellent fatigue resistance of Nd-modified Bi₄Ti₃O₁₂ materials.     

Effects of molten salt synthesis (MSS) parameters on the morphology of Sr3Ti2O7 and SrTiO3 seed crystals

A two-step molten salt synthesis process was utilized to fabricate Sr₃Ti₂O₇ and SrTiO_3. High aspect ratio SrTiO₃ seed crystals were developed by optimizing processing conditions such as temperature, salt-to-oxide ratio, and flux type in a systematic fashion. Sr₃Ti₂O₇ seeds were synthesized at temperatures ranging from 1050–1350°C, using salt-to-oxide ratios of 3:1, 1:1, and 1:3, and various salt types, including NaCl, KCl, and a 1:1 combination of NaCl and KCl. Sr₃Ti₂O₇ seeds synthesized at 1250°C with a 1:1 salt-to-oxide ratio in 100% NaCl salt resulted in a majority of higher aspect ratio platelets and elongated platelets as opposed to lower aspect ratio cubic-like and tetragonal-like morphologies. The seeds were 10–40 μm in length with aspect ratios of highly elongated platelets as high as 25:1. A second MSS step was used to synthesize SrTiO₃ seeds of the proper composition by TiO₂ addition to the Sr₃Ti₂O₇ seeds and heat treatment at 1100°C. These studies showed that highly anisotropic SrTiO₃ seeds could be produced at 1250°C using a 1:1 salt-to-oxide ratio in 100% NaCl flux. XRD studies of the resulting SrTiO₃ seeds revealed that the increase in aspect ratio for these particular seeds also resulted in the enhancement of (200) peaks, which are of major interest for texturing of PMN-PT.     

磁性Fe3O4纳米粒子的合成及表征

纳米Fe3O4是一种多功能磁性材料。用水解法制备Fe3O4纳米颗粒,产物特性的主要影响因素有熟化温度﹑Fe2 与Fe3 的摩尔比和滴定终点的pH值。用正交实验确定适宜的工艺条件,Fe2 与Fe3 的摩尔比为1∶1.75,恒温熟化温度为80℃,滴定终点的pH值=11,在此条件下可合成粒径分布在0.1μm以下占95.53%磁性Fe3O4纳米粉体。采用X射线衍射仪(XRD)、透射电镜(TEM)及振动样品磁强计(VSM)对优化实验产物的分析表明,所制备的纳米粒子属单相立方晶型,平均粒径为56nm,纯度高,具有超顺磁性。     

Laser ablation preparation and property of bismuth-layer-structured SrBi2Ta2Ta2O9 and Bi4Ti3O12 ferroelectric thin films

Abstract

Bismuth-layer-structured ferroelectric thin films, SrBi₂Ta₂O₉ and Bi₄Ti₃O₁₂, have been prepared by laser ablation method on both Pt sheets and Si wafers at low temperatures of 400 ～ 500°C. These thin films have been characterized by XRD, XPS, AFM, C-V, D-E hysteresis and J-V measurement. SrBi₂Ta₂O₉ thin films have a good (105) preferential orientation, and Bi₄Ti₃O₁₂ thin films have (117) and c-axis orientation on these substrates. Ferroelectric film-SiO₂-Si structures show good C-V hysteresis curve owing to Si surface potential controlled by the D-E hysteresis. D-E hysteresis is obtained in Bi₄Ti₃O₁₂ thin film prepared on Pt sheet, and the remnant polarization and the coercive force are 7.5 μC/cm² and 72 kV/cm, respectively.     

Sol-Gel Synthesis and Sensing Study of Perovskite CaCu3Ti4O12 Nanopowders

CaCu₃Ti₄O₁₂ nanopowders were fabricated by a facile effective sol-gel route using tetrabutyl titanate, calcium acetate and cupric nitrate as precursors. The intermediate xerogel was characterized by thermal analyzer and the products with different calcination temperature were then studied by IR spectrum. Further X-ray diffraction, transmission electronic microscopy, high-resolution transmission electron microscopy and energy dispersive X-ray spectrum were used to characterize the prepared CaCu₃Ti₄O₁₂ nanopowders. Additionally, the obtained CaCu₃Ti₄O₁₂ nanopowders were investigated as a gas sensitive material responding to ethanol atmosphere, and it showed high sensitivity for ethanol gas.     

The Effect of La-Doped Bi4Ti3O12 Buffer Layer on Crystallinity and Ferroelectric Properties of PbZr0.58Ti0.42O3/Bi3.25La0.75Ti3O12 Multilayered Thin Films

PbZr_0.58Ti_0.42O₃ (PZT) ferroelectric thin films with Bi_3.25La_0.75Ti₃O₁₂ (BLT) buffer layer of various thickness were fabricated on Pt/TiO₂/SiO₂/p-Si(100) substrates by rf-magnetron sputtering method. The pure PZT film showed (111) preferential orientation in the XRD patterns, and the PZT/BLT films showed (110) preferential orientation with increasing thickness of the BLT layer. There were no obvious diffraction peaks for the BLT buffer layer, for its thin thickness in PZT/BLT multilayered films. There were the maximum number of largest-size grains in PZT/BLT(30 nm) film among all the samples from the surface images of FESEM. The growth direction and grain size had significant effects on ferroelectric properties of the multilayered films. The fatigue characteristics suggested that 30-nm-thick BLT was just an effective buffer layer enough to alleviate the accumulation of oxygen vacancies near the PZT/BLT interface. The comparison of these results suggests that the buffer layer with an appropriate thickness can improve the ferroelectric properties of multilayered films greatly.     

Structural and Multiferroic Properties of Bi3.4La0.6Ti3O12/CoFe2O4 Composite Thin Films

Bi_3.4La_0.6Ti₃O₁₂ and CoFe₂O₄ were synthesized by chemical solution route, and Bi_3.4La_0.6Ti₃O₁₂/CoFe₂O₄ multilayers were deposited by spin coating on Pt substrate. X-ray diffraction of multilayer structures reveals composite-like polycrystalline film. Leakage current is less than 10^?5 A at electric field < 90 KV/cm and follows the Ohmic behavior. Dielectric response shows relaxation and the loss (tan δ) is below 3% at 10⁶ Hz. Room temperature ferrroelectric polarization (P_r) = 20.2 μC/cm² and ferromagnetic memory (M_r) = 46.5 emu/cm³ has been obtained. Co-existence of FE and FM response can be attributed to stress and different permeability and permittivity involved in multilayer structures.     

Thermal Conductivity of Nano ZnO Doped CaFe2O4

The research objective of this study was to examine whether Zn was an effective doping element for thermal conductivity. Ca_1-xZn_xFe₂O₄ (x = 0.0–0.5) were synthesized by solid state reaction method. The XRD results showed that all samples were mixed phase of CaFe₂O₄ and ZnFe₂O₄. The structure of Ca_1-xZn_xFe₂O₄ (x = 0.0–0.5) belonged to a group of an orthorhombic system (space group: Pbnm). It was observed that all the samples of Ca_1-xZn_xFe₂O₄ (x = 0.0–0.5) had positive Seebeck coefficient as shown on p-type semiconductor behavior. Thus thermal conductivity tended to decrease with increasing x value. The Ca_0.6Zn_0.4Fe₂O₄ showed lowest thermal conductivity of 6.52 W m^?1 K^?1 at 473 K, which was lower than 50.81% of CaFe₂O₄. These results suggested that Zn was an effective doping element for improving the thermal conductivity of Ca_1-xZn_xFe₂O₄.     

Ferroelectric Properties of (Bi, Sm)4Ti3O12 (BST) Thin Films Fabricated by a Metalorganic Solution Deposition Method

Ferroelectric properties of samarium substituted Bi₄Ti₃O₁₂ films, Bi_3.15Sm_0.85Ti₃O₁₂ (BST), were evaluated for use as lead-free thin film ferroelectrics for FeRAM applications. The BST films were fabricated on the Pt/Ti/SiO₂/Si(100) substrates by a metalorganic solution deposition method. The measured XRD patterns revealed that the BST films showed only a Bi₄Ti₃O₁₂-type phase with a random orientation. The BST film capacitors showed excellent ferroelectric properties. For the film capacitor annealed at 700C, 2P_r of 64.2 C/cm² and 2E_c of 101.7 kV/cm at applied electric field of 150 kV/cm were observed. The capacitor did not show any significant fatigue up to 1.5 × 10⁸ read/write switching cycles at a frequency of 1 MHz, which suggests that the samarium should be considered for a promising lanthanide elements to make a good thin ferroelectric film for memory applications.     

Integration and characterization of MFISFET using Pb5Ge3O11

Abstract

The first MFIS FETs PMOS using Pt/Pb₅Ge₃O₁₁/ZrO₂/n-Si structure has been successfully fabricated. The PGO thin film was deposited by spin on method. Single phase PGO with strong c-axis orientation and low leakage current was obtained on ZrO₂ substrate. Pt was used as top electrode and the gate stack was dry etched using chlorine chemistry. Using CMOS compatible process, the integration of MFIS FETs is simple and reliable. I_D-V_G and I_D-V_D were characterized on 10 × 10 μrn (L × W) devices. The memory window obtained is about 1.3V with 200nm PGO and 13nm ZrO₂. It is also found that memory window is less dependent on device sizes.     

Dielectric behavior of Bi2/3Cu3Ti4O12 ceramic and thick films

The paper reports on synthesis, sintering and microstructure of Bi_2/3Cu₃Ti₄O₁₂, a lead-free, high-permittivity material with internal barrier layer capacitor behavior. Complex impedance and capacitance of the ceramic and thick films were studied as a function of frequency (10 Hz–2 MHz) and temperature (−170 to 400°C). Dc electrical conductivity of the samples was measured in the temperature range 20–400°C. Broad and high maxima of dielectric permittivity versus temperature plots were observed reaching 60,000 for ceramic and 5,000 for thick films. The maxima decrease and shift to higher temperatures with increasing frequency. Two arcs ascribed to grains and grain boundaries were found in the plots of imaginary part versus real part of impedance. Analysis of the impedance spectra indicates that Bi_2/3Cu₃Ti₄O₁₂ ceramic could be regarded as electrically heterogeneous system composed of semiconducting grains and less conducting grain boundaries. The developed thick film capacitors with dielectric layers based on Bi_2/3Cu₃Ti₄O₁₂ exhibit dense microstructure, good cooperation with Ag electrodes, high permittivity up to 5,000 and relatively low temperature coefficient of capacitance in the temperature range 100–300°C. Broad maxima in the dielectric permittivity versus temperature curves may be attributed to Maxwell–Wagner relaxation.     

Preparation of Epitaxial Bi4Ti3O12 Thin Films on LaAlO3(012) Substrates by a Spin Coating-Pyrolysis Process

Bismuth titanate Bi₄Ti₃O₁₂ thin films were prepared on LaAlO₃(012) substrates by a spin coating-pyrolysis process using metal naphthenates as starting materials. The c-axis oriented Bi₄Ti₃O₁₂ thin films, which contained no second phases as –2 scans, were obtained by heat-treatment in air at temperatures of 600°C and above. X-ray diffraction pole-figure analysis showed that the Bi₄Ti₃O₁₂ thin film has an epitaxial relationship with the LaAlO₃ substrate.     

Thermoelectricity of p-Fe2O3-SO3-SiO2-others and n-Fe2O3-SiO2-CuO-others

Thermoelectric minerals have been found at Loei Province, in the northeastern part of Thailand. Local mineral specimens were prepared in the powders and bulk solids form by crushing, calcination and annealing, pressure and sintering, cutting and polishing. Mineral samples were used to analyze the composition and phase, determine the thermoelectric property and efficiency, design and construct a thermoelectric generator. Chemical composition and phase identification of powder samples were analyzed by the x-ray fluorescence (XRF) and x-ray diffraction (XRD), respectively. XRF and XRD results indicated that the mineral samples comprised the SO₃-CaO-SiO₂-others, Fe₂O₃-SO₃-SiO₂-others, Fe₂O₃-SiO₂-others and Fe₂O₃-SiO₂-CuO-others. From the thermoelectric property and efficiency determinations, the p-SO₃-CaO-SiO₂-others, p-Fe₂O₃-SO₃-SiO₂-others, n-Fe₂O₃-SiO₂-others and n-Fe₂O₃-SiO₂-CuO-others bulks were found to exhibit the thermoelectric figure of merit in orders of 10^?14, 10^?11, 10^?14 and 10^?13 K^?1, respectively. A fabricated thermoelectric generator made from ten pairs of p-Fe₂O₃-SO₃-SiO₂-others and n-Fe₂O₃-SiO₂-CuO-others legs that can be provided the open circuit voltage and short circuit current up to 48.30 mV and 0.14 μA for a temperature difference of 39.80 K at room temperature, respectively. While the internal resistance decreased and reached a value of 665 kΩ.     

Effect of B2O3 and CuO on the sintering temperature and microwave dielectric properties of the BaTi4O9 ceramics

The effect of B₂O₃ and CuO on the sintering temperature and microwave dielectric properties of BaTi₄O₉ ceramics was investigated. The BaTi₄O₉ ceramics were able to be sintered at 975^∘C when B₂O₃ was added. This decrease in the sintering temperature of the BaTi₄O₉ ceramics upon the addition of B₂O₃ is attributed to the formation of BaB₂O₄ second phase whose melting temperature is around 900^∘C. The B₂O₃ added BaTi₄O₉ ceramics alone were not sintered below 975^∘C, but were sintered at 875^∘C when CuO was added. The formation of BaCu(B₂O₅) second phase could be responsible for the decrease in the sintering temperature of the CuO and B₂O₃ added BaTi₄O₉ ceramics. The BaTi₄O₉ ceramics containing 2.0 mol% B₂O₃ and 5.0 mol% CuO sintered at 900^∘C for 2 h have good microwave dielectric properties of ε_r = 36.3, Q× f = 30,500 GHz and τ_f = 28.1 ppm/^∘C