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.     

Epitaxial Growth and Luminescent Properties of Mn2+-Activated ZnGa2O4 Films

The epitaxial growth and properties of Mn²⁺-doped ZnGa₂O₄ thin films on various single crystal substrates using pulsed laser deposition were investigated. Control of Zn/Ga stoichiometry required the use of a mosaic ZnGa₂O₄/ZnO ablation target to compensate for Zn loss due to evaporation. The photoluminescent intensity was a strong function of the Zn/Ga ratio, and also correlated with changes in the surface morphology. Superior photoluminescent intensity was attained from slightly Zn-deficient films which exhibit distinctive worm-like surface features. Enhanced photoluminescent intensity was observed in epitaxial films as compared to randomly-oriented polycrystalline deposits on glass substrates, suggesting an adverse effect of grain boundaries on luminescence properties.     

The preparation of ZnGa2O4 doped with Mn‐Mg and Tm for green and blue phosphors

Phosphor powders of zinc gallate (ZnGa₂O₄) with Mg and Mn for green and Tm‐Mg for blue luminescence were prepared by solid state reaction method for their improved luminescent properties. Green‐luminescence emitting ZnMnGa₂O₄ reached maximum intensity at Mn = 0.005 mol% and further improvement was achieved by the addition of Mg²⁺. Tm‐Mg based zinc gallate phosphor exhibited a strong blue emission, centered at ∼420 nm with the maximum intensity achieved for 0.003 mol% of Mg and 0.015 mol% of Tm. This study established the possibilities of controlling the luminescent characteristics of zinc gallate by adding various elements. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

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.     

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.     

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.     

Fabrication of amorphous bulk and multi-phase ceramics by melting method in the HfO2-Al2O3-Gd2O3-Eu2O3system

Ceramics have generally been fabricated from powders by shape forming & sintering methods except for glasses and glass ceramics. Glasses and glass ceramics can be fabricated by melting methods. The melting method has not only higher productivity but also higher shape forming ability than powder processes via forming & sintering methods. Thus we have reinvestigated melting methods in binary and ternary oxides systems to fabricate amorphous bulk ceramics and bulk nano composites. We have successfully fabricated amorphous phases by simple melt solidification methods in ternary eutectic melts in the HfO₂-Al₂O₃-Gd₂O₃system. The present study demonstrates the formation of the amorphous phases in quaternary systems HfO₂-Al₂O₃-Gd₂O₃-Eu₂O₃. Furthermore, we have also succeeded to fabricate nano-structured bulk ceramics, which consisted of constituent oxide grains with 20–100 nm in size, by post annealing of the amorphous phase.     

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.     

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.     

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.     

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.     

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     

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.     

Effects of Substrate and Annealing Temperatures on the Characteristics of SrBi4Ti4O15 Thin Films

In this study, radio frequency (RF) sputtering was used as the method and the layer-structured bismuth compound of SrBi₄Ti₄O₁₅ + 4 wt% Bi₂O₃ ferroelectric ceramic was used as the target to deposit the SrBi₄Ti₄O₁₅ (SBT) thin films. The addition of excess Bi₂O₃ content in the target ceramic was used to compensate the vaporization of Bi₂O₃ during the sintering and deposition processes. SBT ferroelectric thin films were deposited on Pt/Ti/SiO₂/Si under optimal RF magnetron sputtering parameters with different substrate temperatures for 2 h. After that the SBT thin films were post-heated using rapid temperature annealing (RTA) method. The dielectric and electrical characteristics of the SBT thin films were measured using metal-ferroelectric-metal (MFM) structure. From the physical and electrical measurements of X-ray diffraction pattern, scanning electronic microscope (SEM), I-V curve, and C-V curve, we had found that the substrate temperature and RTA-treated temperature had large influences on the morphology, the crystalline structure, the leakage current density, and the dielectric constant of the SBT thin films.     

热处理制度对机械化学法合成LiMn2O4的影响

以Li2CO3和Mn3O4为原料,采用机械化学法合成了尖晶石LiMn2O4.考察了热处理温度和时间对LiMn2O4电化学性能的影响.720℃下热处理2 h、6 h和10h所得样品的首次放电比容量分别为124.5 mAh/g、124.6 mAh/g和126.3 mAh/g.在400℃、600℃、720℃和800℃下热处理6 h后得到的样品的首次放电比容量分别为120.6 mAh/g、124.4 mAh/g、124.6 mAh/g和128.6 mAh/g,经过10次循环后,比容量下降的幅度分别为13.8%、11.5%、9.5%和6.5%.适宜的热处理制度为:800℃热处理6 h.     

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.     

二次烧结制备的尖晶石LiMn2O4的性能

用高温固相法二次烧结制备了锂离子电池正极材料尖晶石LiMn2O4.利用XRD、EDS和SEM等方法及激光粒度分析仪,研究了LiMn2O4的晶体结构、粒径及形貌与电化学性能的关系.与一次烧结的样品比较,二次烧结的样品粒径分布更集中于25～35μm,结晶更完全,电化学性能及循环稳定性更好.二次烧结后掺杂Zn(Ac)2的样品,在常温和高温(55℃)下的首次放电比容量分别为112.8 mAh/g和113.5 mAh/g,经过50次循环后,容量保持率分别为99.7%(常温)和94.5%(高温,55℃).     

Synthesis and properties of ferroelectric Si-doped (Bi, Nd)4Ti3O12 thin films by chemical solution deposition

Ferroelectric Si-doped (Bi,Nd)₄Ti₃O₁₂ thin films have been prepared on Pt/TiO_x/SiO₂/Si substrates through metal-organic compounds by the chemical solution deposition. The Bi_3.25Nd_0.75Ti_2.9Si_0.1O₁₂ (BNTS) precursor films were found to crystallize into the Bi-layered perovskite Bi₄Ti₃O₁₂ single-phase above 600^∘C. The synthesized BNTS films revealed a random orientation having a strong 117 reflection. The BNTS thin films prepared between 600^∘C and 700^∘C showed well-saturated P-E hysteresis loops with P _r of 13–14 μ C/cm² and E _c of 100–110 kV/cm at an applied voltage of 5 V. The surface roughness of the BNTS thin films was improved by Si doping compared with that of undoped Bi_3.35Nd_0.75Ti₃O₁₂ films.     

The Effects of Lithium and Oxygen Contents Inducing Capacity Loss of the LiMn2O4 Obtained at High Synthetic Temperature

Well-crystallized LiMn₂O₄ has been synthesized at different calcination temperatures using the melt-impregnation method. The lattice constant of LiMn₂O₄ increased with increasing calcination temperatures. Li/LiMn₂O₄cells calcined at lower temperatures (700–800°C) showed excellent cycling performances at room temperature. However, those cells calcined at higher temperature (850–900°C) exhibited abrupt capacity loss in the early stage and very poor cycle retention rate (>65%) after 50 cycles. It was considered that poor cycle performance of the spinels obtained at high temperature resulted from the lithium sublimation and oxygen deficiency during synthetic process. We found that above two factors, lithium sublimation and oxygen deficiency, were the commonly important factors to induce capacity loss in the Li/LiMn₂O₄ system, especially obtained at high synthetic temperature.     

溶液燃烧法合成11ScSZ-2Mn_2O_3电解质粉体及其应用

采用硝酸盐-甘氨酸溶液燃烧法合成了(ZrO2)0.87(Sc2O3)0.11(Mn2O3)0.02(11ScSZ-2Mn2O3)粉体,通过X射线衍射仪(XRD)、透射电镜(TEM)、场发射扫描电镜(FESEM)及氮气吸附等手段对粉体进行表征。结果表明,所合成的11ScSZ-2Mn2O3粉体具有单一立方结构,比表面积达28.6m2/g,粒度均匀。非等温和等温烧结测试均表明该粉体具有良好的烧结活性,可在1200℃下烧结致密化。以11ScSZ-2Mn2O3粉体为原料配制电解质粉体浆料,采用浸渍-提拉法在NiO-氧化钇稳定氧化锆(YSZ)阳极基体上制备了电解质薄膜,在1250℃下实现了负载型薄膜的烧结致密化,与La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF)阴极组装了单元电池Ni-YSZ/11ScSZ-2Mn2O3/LSCF。该单元电池在中温下以H2为燃料表现出良好的电性能输出,在操作温度为650℃和700℃下的最大输出功率密度分别为0.55W/cm2和0.90W/cm2。