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.     

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.     

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.     

Facile synthesis of superparamagnetic Fe3O4 nanoparticles just using ferric citrate and water

Fe₃O₄ nanoparticles were synthesized by a facile one-pot hydrothermal process just using ferric citrate and water without any additional reagent and post-treatment. The temperature of hydrothermal reaction had important influence on the crystallinity and magnetic property of Fe₃O₄ samples. Fe₃O₄ sample synthesized at 200 °C for 24 h showed a narrow size distribution (4 to 8 nm in diameter), and exhibited apparent superparamagnetism with saturated magnetization of 55.1 emu/g. The narrow size distribution and superparamagnetism were the interesting features of these Fe₃O₄ nanoparticles.     

Characteristics of ZnGa2O4 phosphors synthesized by solution combustion method

ZnGa₂O₄ phosphors were synthesized by both SCM (solution combustion method) and SSRM (solid state reaction method). The characteristics of the both ZnGa₂O₄ phosphors were investigated by TGA (Thermogravimetric analysis), SEM (scanning electron microscope), BET (Brunauer Emmett Teller), PL (photoluminescence) and XRD (X-ray diffraction). The particle size of SCM phosphor was about one-hundredth of SSRM phosphor. The PL intensity of SCM phosphor was about 1.5 fold higher than that of SSRM phosphor. The SCM phosphor was also tried to be doped with Mn⁺² ions. The highest PL peak was observed with Mn⁺² ions of 0.003 mole fraction. The peak was shifted from blue (470 nm) to green (513 nm) color. These results might be very useful for high efficiency phosphors for displays such as field emission displays and plasma display panels.     

Grain growth kinetics of LiMn2O4 nanocrystals during calcining process

ABSTRACT

LiMn₂O₄ nanocrystal was synthesized by coprecipitation using Mn(CH₃COO)₂ and LiOH as raw materials. Samples were characterized by thermo gravimetric/differential scanning calorimetry, X-ray diffraction and transmission electron microscope. Effort of calcination temperatures (600, 650, 700, 750 and 800°C) on grain size of LiMn₂O₄ was discussed. Results indicated that temperature had positive correlation with grain size. Grain growth kinetics of LiMn₂O₄ nanocrystal was simulated with a conventional model and an isothermal model. Simulation results indicated that the isothermal model was suitable to fit with data, implying the important roles of diffusion and surface reaction.     

Defect Chemistry of Y Doped BaTiO3

Defect chemistry of Y doped BaTiO₃ was investigated as a function of the Ba/Ti ratio. When the Ba/Ti ratio was greater than unity, Y^{3 +} was substituted for the normal Ti site and the equilibrium conductivity showed a strong evidence of acceptor-doped behavior. With the Ba/Ti ratio < 1, Y^{3 +} was substituted for the Ba site and the equilibrium conductivity showed donor-doped behavior. In the case excess Y₂O₃ was added to the stoichiometric BaTiO₃(Ba/Ti = 1), the conductivity profile showed a donor-doped behavior at low concentrations (< 1.0 mol%), whereas, at higher donor levels (> 2.0 mol%), the equilibrium conductivity minimum shifted toward lower Po₂, indicating acceptor doped behavior.     

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.     

ZnGa2O4 thin films fabricated by Sol-gel spinning coating process

ZnGa₂O₄ thin film phosphors have been synthesized on ITO coated glass and soda-lime glass at a firing temperature of 500^∘C and an annealing temperature of 500^∘C and 600^∘C via a chemical solution method using Zinc acetate dihydrate, Gallium nitrate hydrate and 2-methoxiethanol as a solution. XRD patterns of the film phosphors synthesized showed the peaks of ZnGa₂O₄ crystalline phases. AFM surface morphologies of the ZnGa₂O₄ thin film phosphors revealed marked differences according to an annealing temperature of 500^∘C and 600^∘C under an annealing atmosphere (3% H₂/Ar). On the other hand, the sheet resistance of ZnGa₂O₄ thin film phosphors, which were measured by four-point probe instrument, was approximately 5.76 Ω /square and 7.86 Ω /square with annealing temperature, respectively. The ZnGa₂O₄ thin film phosphors exhibited blue emission spectra with peak wavelength of 434 nm and 436 nm by ultra-violet excitation around 230 nm.     

Influence of B2O3/SiO2 Ratio on the Fabrication of Nd:YAG Ceramics

B₂O₃/SiO₂ are used as composite sintering aids to fabricate Nd:YAG ceramics by solid-state reaction and vacuum sintering method at 1750°C for 5h using Nano-Al₂O₃, Y₂O₃, Nd₂O₃ as starting materials. In this article, we focus on the influence of B₂O₃/SiO₂ ratio on grain size, porosity and relative density. Finally, with the increase of B₂O₃/SiO₂ ratio, the density and shrinkage rate of transparent ceramics increase, the grain size becomes uniform and the porosity reduces, for the reason that B³⁺ begins to vaporize at 1300°C and is reduced to trace levels by 1600°C. The best B₂O₃/SiO₂ ratio is 4: 1.     

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.     

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.     

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     

Characterization and Electrochemical Studies of LiMn2O4 Cathode Materials Prepared by Combustion Method

A combustion method using urea as a fuel has been developed for the synthesis of the spinel LiMn₂O₄ around 500°C. Physical features of the products were identified by X-ray photoelectron spectroscopy, X-ray diffractometry, Raman scattering and FTIR spectroscopy. Cells were fabricated with Li//LiMn₂O₄ and C//LiMn₂O₄ in nonaqueous organic electrolyte and their performances were studied. A kinetic profile for diffusion of Li ions in the composite matrix was developed and tested.     

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.     

Photoluminescence and photocurrent characteristics of Eu2 + activated MAl2O4 (M = Ba, Ca, Sr) phosphors

Photoluminescence and photocurrent characteristics of Eu^{2 +} activated MAl₂O₄ (M = Ba, Ca, Sr) phosphors during and after Ultraviolet ray and visible light irradiation have been investigated. The photoluminescence (PL) and the photocurrent (PC) of the phosphors, in order to elucidate the relationship between the PL and the PC, were measured simultaneously on the same samples within a specially designed measuring box. Composition effects, such as a presence of Dy^{3 +} as a co-activator and Al-rich composition on the PL and PC characteristics have been investigated. Also, sensing characteristics on UV and visual light have been tested. The simultaneous measurement of PL and PC on the same sample clearly indicated that the presence of co-activator and vacant site, namely Al-rich composition, acted as a hole trap; the introduction of co-activator and vacant site decreased the PC and increased the PL during and after UV and visible light irradiation, whose PC was much lower than that of MAl₂O₄ with only Eu^{2 +} as an activator. The electrical intensity affected on the PL characteristics after UV and visual light irradiation(afterglow); with increasing in the electrical intensity, the afterglow lasted more longer and intensively. The PC of MAl₂O₄ showed a good proportional relationship to UV and visible light intensity. Especially, SrAl₂O₄ showed an excellent linearity within 1–5 mW/cm², but showed somewhat delayed response and hysterisis as seen in CdS photoelectric cell.     

YBa2Cu3O7-x/SrTiO3//LaAlO3 heterostructures obtained by injection MOCVD

Abstract

YBa₂Cu₃O_7-x /Ba_xSr_1-xTiO₃ /LaAlO₃ heterostructures can be used as a basis for devices with voltage control in microwave circuits.

Ba_xSr_1-xTiO₃ (x=0–0.1) (BST) thin films have been epitaxially grown on LaAlO₃ substrates using injection MOCVD. The excellent crystalline quality of the obtained BST films can be proven by a FWHM of <0,2° for the rocking curve of the (002) BST reflection. An AFM study revealed flat surfaces, showing a surface roughness R_s as low as 1nm. YBa₂Cu₃O_7-x/Ba_xSr_1-x TiO₃//LaAlO₃ heterostructures were than optimised. The YBa₂Cu₃O_7-x (YBCO) layers obtained on Ba_xSr_1-xTiO₃ films are epitaxial with a FWHM of 0.45° for the (005) YBCO rocking curve and display very promising superconducting properties of T_c=92K.

Finally the microwave properties of the superconducting films were studied. For YBa₂Cu₃O_7-x layers directly deposited on LaAlO₃, surface resistance values of 0,32mΩ were obtained, while for YBa₂Cu₃O_7-x /SrTiO₃//LaAlO₃ heterostructures, higher values of 1mΩ at 8.5GHz were measured.     

Predication of Thermal Conductivity of Mg2X (X = Ge and Sn) by Molecular Dynamics

Molecular dynamics (MD) simulations of elastic and thermal properties of Mg₂X (X = Ge and Sn) based on anti-fluorite structure (CaF₂) at temperature range 300?700 K were presented. The MD simulation in this study involving the Morse?type potential functions, and the Busing–Ida potential to determine the interatomic interaction among cluster atoms size 4×4×4 unit cells of 768 atoms {512?Mg^1.2+, 256?(Ge, Sn)^2.4?}. The potential parameter functions of the cluster atoms were indicated by random numerical method and fit lattice parameter from the experimental data obtained at room temperature. The calculation of lattice parameter, pressure, temperature and energy contributes to evaluation of the elastic properties. The results showed that Mg₂Ge had better elasticity than Mg₂Sn. On the other hand, Mg₂Sn had less thermal conductivity than Mg₂Ge. Since thermal conductivity decreases with increasing temperature, the interesting feature of thermal conductivity is particulary useful to enhance thermoelectric performance of materials.     

Characterization of the CeO2 thin films for insulation layer and Pt/SrBi2Ta2O9/CeO2/Si MFISFET structure

Abstract

CeO₂ and SrBi₂Ta₂O₉ (SBT) thin films for MFISFET (metal-fcrroelectrics-insulator-semiconductor field effect transistor) were deposited by rf sputtering and pulsed laser deposition method, respectively. The effects of oxygen partial pressure during deposition for CeO₂ films were investigated. The oxygen partial pressure significantly affected the preferred orientation, grain size and electrical properties of CeO₂ films. The CeO₂ thin films with a (200) preferred orientation were deposited on Si(100) substrates at 600°C. The films deposited under the oxygen partial pressure of 50 % showed the best C-V characteristics among those under various conditions. The leakage current density of films showed order of the 10^?7～10^?8 A/cm² at 100 kV/cm. The SBT thin films on CeO₂/Si substrate showed dense microstructure of polycrystalline phase. From the C-V characteristics of MFIS structure composed of the SBT film annealed at 800°C, the memory window width was 0.9 V at ±5 V. The leakage current density of Pt/SBT/CeO₂/Si structure annealed at 800°C was 4×10^?7 A/cm² at 5 V.     

Effect of Precursor Concentration on Physical Properties of Cube-Like Zn2SnO4 Powders Synthesized by Co-Precipitation Method

Cube-like Zinc stannate (Zn₂SnO₄) spinel powders were synthesized by co-precipitation method using chloride starting precursors of zinc and tin. The influence concentration of precursors on relevant physical properties of Zn₂SnO₄ was investigated by increasing concentration of precursor material at 0.1 to 0.4 M (Zn:Sn at ratio 1:1). Structural properties of as-synthesized and Zn₂SnO₄ crystal were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray absorption spectroscopy (XAS). The results indicate that as-prepared material without calcination process is in cubic symmetry of zinc hydroxy stannate (ZnSn(OH)₆) affirmed by SEM and XRD results. Meanwhile, spinel phase of Zn₂SnO₄ with strong crystalline and eminent cubic structure can be achieved after calcination at 1000°C. Homogenous dispersion, high crystallinity and good cubic structure of Zn₂SnO₄ powders are occurred at higher concentration of precursors. Moreover, the oxidation state of these samples were investigated by the Zn K-edge and Sn L3-edge X-ray absorption near edge structure (XANES) using the synchrotron radiation light source. The analyses of XANES spectra revealed that the oxidation state of Zn was +2 and Sn valence was +4 in all Zn₂SnO₄ samples, which well corresponds to the theoretical values.