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.     

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 Sr-Bi-Ta Oxide Films of Cubic Fluorite-Like Structure

Epitaxial Sr-Bi-Ta oxide films of a cubic fluorite-like structure were grown by pulsed laser deposition. As the laser fluence increased, the lattice constant decreased. It was revealed that the Ta ion concentration was closely related with the change in the lattice constant. From selected area electron diffraction measurements, it was observed that the films had a superstructure which seemed to come from ordering of metal ions.     

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.     

不同锂锰比尖晶石型LiMn2O4的结构与电化学性能的分析

分析了系列不同锂锰比对尖晶石型LiMn2O4性能的的影响。并对样品进行TG-DTA(热重/差热分析仪)、XRD(X射线衍射光谱)、SEM(扫描电镜)与电性能测试。研究结果表明:Li∶2Mn为1.00～1.50时,都可以得到尖晶石结构的LiMn2O4;当Li∶2Mn比值为1时,LiMn2O4的晶粒单体形态表现为规则的八面体状;随Li∶2Mn比值增大,LiMn2O4晶胞轴长有变小趋势,电化学稳定性有一定增强,比容量和电循环性能均有所改善,Li∶2Mn比值约为1.04～1.05时,其电化学性能表现较好;随着锂锰比的增加,杂相也相应增加,LiMn2O4由规则粒状渐变为团块状。由于杂质相含量的增加及LiMn2O4晶格变形增强,当Li∶2Mn比大于1.2时,电化学性能也明显变差。     

Growth and characterization of non-c-axis-oriented SrBi2Ta2O9 epitaxial thin films on Si(100) substrates with SrRuO3 bottom electrodes

Abstract

We have successfully grown non-c-axis-oriented epitaxial ferroelectric SrBi₂Ta₂O₉ (SBT) films with (116) and (103) orientations on Si(100) substrates using epitaxial (110)- and (111)-oriented SrRuO₃ (SRO) bottom electrodes, respectively. The SRO orientations have been induced by coating the Si(100) substrates with epitaxial YSZ(100) and MgO(111)/ YSZ(100) buffer layers, respectively. All films were sequentially grown by pulsed laser deposition. Specific in-plane orientations of the epitaxial SBT films were found, which are in turn determined by specific in-plane orientations of the epitaxial SRO bottom electrodes. These include a diagonal rectangle-on-cube epitaxy of SRO(110) on YSZ(100) and a triangle-on-triangle epitaxy of SRO(111) on MgO(111).     

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.     

Effect of Strain Gradation on Luminescence and Electronic Properties of Pulsed Laser Deposited Zinc Oxide Thin Films

ZnO thin films were grown by ablation of a ZnO ceramic target using pulsed excimer laser (KrF) under 1 mTorr oxygen partial pressure over (0001) -Al₂O₃ substrates held at 750_C. Highly c-axis oriented (0002) ZnO films with visible range optical transparency over 80% were obtained. Inhomogeneous distribution of strain in the film growth direction was studied by line shape analysis of X-ray diffraction and broad luminescence features centered on near band edge transition at 3.3 eV. Strain in the film adversely affects optical gain and excitonic threshold of UV emission. Post-growth oxygen annealing of films at 850°C for 1 h reduces strain and associated defects at ZnO film interface with (0001) Al₂O₃ substrate. FWHM of X-ray rocking curves show corresponding lowering from 12.5 arc min to 9.0 arc min signifying improved ZnO crystal quality. -rocking curves show line features with two superimposed peaks belonging to interfacial layer and bulk ZnO film. Graded strain in ZnO film is related to differently oriented interfacial layer formed at inception stage of film growth. Decrease in conductivity of annealed ZnO films show that O₂-vacancies are primary defects. Formation of strain free (0002) oriented optical quality ZnO films based on combined process of growth in low O₂ pressure and post growth anneal at high O₂ pressure is proposed for UV-optoelectronic applications.     

Effect of Oxygen Plasma on Growth, Structure and Ferroelectric Properties of SrBi2Ta2O9 Thin Films Formed by Pulsed Laser Ablation Technique

Growth of SrBi₂Ta₂O₉ (SBT) thin films has been carried out in the presence of O₂-plasma created by applying a potential at an auxiliary ring electrode placed near the substrate. Effect of plasma excitation potential and polarity, especially negative polarity, on the formation of a proper SBT phase at 700°C and in modifying crystallite orientation and microstructure of SBT films over (1 1 1) oriented Pt film coated over TiO₂/SiO₂/Si(1 0 0) substrates has been demonstrated. Preferred c-axis orientation of SBT films changes to (a–b) orientation with decrease in plasma excitation potential from –700 to –350 V and eliminates secondary Bi₂Pt phase formation even at 600°C Microstructural study show a 2-dimensional large flat c-oriented crystallites formed at –700 V change to small crystallites in conformity with the changed aspect ratio for crystallites in (a–b) plane parallel to film plane. Spectroscopic ellipsometric results are in agreement with the microstructural data. These affects are attributed to O₂-ion bombardment during film growth which reduces nucleation barrier for growth of crystallites in (a–b) plane. O₂-plasma sustains the cationic species formed by laser ablation, which along with O ₂ ⁺ ions, provide necessary activation energy and enhance the oxidation rates required for SBT phase formation even at 700°C. SBT films grown in O₂-plasma show enhancement in remnant polarization value from 1.2 to 6.6 C/cm² and display ferroelectric properties superior to those formed without plasma. Further O₂-plasma eliminates post deposition annealing step for observance of enhanced polarization values. This study shows O₂-plasma excitation potential could be exploited as a new process parameter in laser ablation growth of ferroelectric oxide thin films.     

球形四氧化三锰合成锰酸锂的性能

分别以湿法沉淀的球形四氧化三锰(Mn3O4)和商业电解二氧化锰(EMD)为锰源合成锰酸锂(Li Mn2O4)。通过杂质含量分析、XRD、SEM和充放电测试等,研究锰源对产物性能的影响。以粒度为10μm的球形Mn3O4为原料合成的Li Mn2O4保留了锰源的物化特征,以1.0 C在3.00~4.35 V充放电,首次放电比容量为117.2 m Ah/g,常温、55℃高温循环100次的容量保持率分别为94.6%和91.0%,高于以EMD为原料合成的Li Mn2O4(分别为87.9%和72.9%)。循环性能的提高,与球形Li Mn2O4的粒度分布集中、比表面积小及杂质含量低有关。     

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.     

BaTiO 3 on YBa 2 Cu 3 O 7 High T C Superconductors-Microwave Properties

We have made both patterned and unpatterned BaTiO 3 on YBa 2 Cu 3 O 7 microwave test structures as well as identical YBa 2 Cu 3 O 7 test structures and characterized them at 3.3 and 35 GHz. In both cases we found that the best unloaded Q values of the test resonators was for devices made from BaTiO 3 coated YBa 2 Cu 3 O 7 . This had led us to conclude that, at low temperatures, BaTiO 3 does not add additional losses to the system and that it may, in addition to being a tunable ferroelectric material, aid in passivating the YBa 2 Cu 3 O 7 ' surface. We present here preparation and measurement details and discuss the direction of future work in this area.     

Epitaxial structure SrBi2Ta2O9<116> /SrTiO3<011> /Ce0.12Zr0.88O2<001> /Si<001> for ferroelectric-gate FET memory

Abstract

Epitaxial thin film growth of SrBi₂Ta₂O₉/SrTiO₃/Ce_0.12Zr_0.88O₂ on Si was studied, and this epitaxial layer structure was applied to fabrication of ferroelectric-gate field effect transistors (FETs). The films were prepared by a pulsed laser deposition technique and epitaxial growth was identified by x-ray diffraction. The devices exhibited excellent electrical performances: Capacitance-voltage characteristic of a metal-ferroelectric-insulator-semiconductor (MFIS) diode showed a retention longer than 10 days and I_d-V_g characteristic of an MFIS-FET showed 1 day retention. It is proved that the crystalline quality of ferroelectric thin films is of great importance to develop integrated devices with high performance.     

Pulsed Laser Deposited Ba(Mg1/3Ta2/3)O3 Microwave Dielectric Thin Films

Ba(Mg_1/3Ta_2/3)O₃ (BMT) microwave dielectric thin films were successfully synthesized by a modified pulsed laser deposition (PLD) process, which includes low temperature (200°C) deposition and high temperature (>500°C) annealing. Crystalline structured BMT thin films were obtained when the PLD-deposited films were post-annealed at a temperature higher than 500°C in oxygen atmosphere. The characteristics of BMT thin film, including crystallinity, grain size, film roughness, and dielectric properties were improved with annealing temperature, achieving dielectric constant K = 23.5 and dissipation factor tan δ = 0.015 (at 1 MHz) for the 800°C-annealed films.     

Growth and characterization of epitaxial SrBi2Ta2O9 films on (110) SrTiO3 substrates

Abstract

SrBi₂Ta₂O₉ (SBT) is an attractive material for nonvolatile ferroelectric memory applications. In this paper we report on the deposition of highly epitaxial and smooth SrBi₂Ta₂O₉ films on (110) SrTiO₃substrates. The films were grown by pulsed laser deposition at temperatures ranging from 600 to 800°C and at various laser fluences from a Bi-excess SBT target. The background oxygen pressure was maintained at 28 Pa during the film deposition. Structural characterization of the films was performed by x-ray diffraction. Atomic force microscopy was used to investigate morphology and growth of the films. The films grew with preferred (115) or (116) orientation. The roughness was of the order of unit cell height. The films display a growth pattern resulting in corrugated film morphology.     

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.     

CoFe2O4/TiO2纳米复合薄膜的制备与磁性

以钛酸丁酯和金属盐酸盐为原料,采用溶胶-凝胶工艺制备了磁性CoFe2O4/TiO2复合薄膜.通过综合热分析(DSC)、X射线衍射仪(XRD)、扫描电镜(SEM)、原子力显微镜(AFM)、偏光显微镜(PLM)观测了复合薄膜的相结构和表面形貌,探讨了薄膜的合成机理,采用振动样品磁场计测量样品的磁性.研究发现,溶胶-凝胶法制得的复合薄膜中,随着热处理温度的升高,两相组分晶体各自析出长大,CoFe2O4均匀地分布在TiO2网状基体中.样品经800℃退火后得到了平整的CoFe2O4/TiO2磁性复合薄膜,晶粒平均粒径大约为19nm.随着热处理温度的升高,复合薄膜的磁性增强.     

用溶胶-凝胶法在LiCo0.05Mn1.95O4表面包覆Al2O3

首次以异丙醇铝为原料,采用溶胶凝胶法在LiCo0.05Mn1.95O4表面包覆了一层稳定的Al2O3膜。用X射线衍射、扫描电镜及其能谱对包覆前后LiCo0.05Mn1.95O4的结构进行了表征,并测试了样品在常温(25 ℃)和高温(55 ℃)时的电化学性能。研究表明,经Al2O3包覆处理后的LiCo0.05Mn1.95O4有效抑制了LiCo0.05Mn1.95O4与电解液之间的恶性相互作用,降低了Mn的溶解,稳定了LiCo0.05Mn1.95O4的结构,改善了LiCo0.05Mn1.95O4的循环性能。并研究了Al2O3不同包覆量对LiCo0.05Mn1.95O4电化学性能的影响,以Al2O3包覆量为0.5 %(质量百分数)的CAl0.5样品的循环性能较优。     

Ti^4＋和Zn^2＋离子复合掺杂对LiNi0.5Co0.2Mn0.3O2性能的影响

以Ni0.5Co0.2Mn0.3（OH）2和Li2CO3为原料,TiO2和ZnO为掺杂剂,制备出不同含量钛锌离子复合掺杂的锂离子电池正极材料LiNi0.5Co0.2Mn0.3O2。用XRD、SEM、恒电流充放电、交流阻抗法和循环伏安方法分别研究了不同掺杂量对LiNi0.5Co0.2Mn0.3O2的结构、形貌和其电化学性能的影响。结果表明3%（摩尔分数）的Ti、Zn离子复合掺杂能有效提高LiNi0.5Co0.2Mn0.3O2的倍率放电能力和循环性能。在1C和2C的充放电倍率下,首次放电容量分别为170.4mAh/g和164.8mAh/g,经过50次充放电循环后容量保持率分别为96.3%和94.7%,具有优良的电化学性能。     

Crystal Growth and Dielectric Properties of New Ferroelectric Barium Titanate: BaTi2O5

Single crystals of the ferroelectric BaTi₂O₅ and BaTiO₃ were prepared from a solution of 33-mol% BaO and 67-mol% TiO₂ by a rapid cooling method. The dielectric constant () and dielectric loss tangent (tan) were measured in a wide temperature range of 10–860 K and in a frequency range of 0.1–3,000 kHz. The along the b-axis of the BaTi₂O₅ crystal, prepared in air, shows a sharp dielectric anomaly reaching 30,000 at the ferroelectric Curie temperature of T_C = 752 K. By contrast, the crystal prepared in a reducing atmosphere shows a diffuse phase transition near T_C = 703 K. The values of and tan are compared between these three crystals consisting of two kinds of BaTi₂O₅ and one BaTiO₃.