对流效应和溶质浓度对KNbO_3晶体界面形貌稳定性的影响

研究了在不同对流形态对ＫＮｂＯ３晶体生长形貌的影响．在温度梯度较小的扩散－平 流区域,晶体以枝蔓晶的形态生长;而在温度梯度较大的扩散－对流区域,生长出的晶体呈现 光滑晶面．通过测定不同区域ＫＮｂＯ３晶体界面附近的溶质浓度分布,从对流效应降低晶体界 面附近的溶质浓度分布的不均匀性的角度研究了对流效应对晶体界面形貌稳定性的影响,证明 对流效应提高了晶体界面形貌稳定性,与晶体界面弥散度的理论计算结果相一致．同时解释了 扩散－对流区域的晶体尺寸大于扩散－平流区域的晶体尺寸的原因．观察并定性地解释了不同 溶质浓度ＫＮｂＯ３形成不同的界面非稳定形貌,当 ＫＮｂＯ３重量百分比为２０ｗｔ％时形成骸晶, ３０ｗｔ％时形成枝蔓晶．     

氧化物溶液表面张力对流速度场研究

利用示踪粒子获得直径为２ｍｍ的环状铂金坩埚内Ｌｉ_２Ｂ_４Ｏ_７＋ＫＮｂＯ_３熔体近坩埚区域的表面张力对流速度场;并从理论上推导出表面张力对流速度场解析表达式,推导结果与实测结果一致．     

Nb2O5对ZTM-Al2O3性能及ZrO2增韧机制的影响

探讨了Ｎｂ_２Ｏ_５对ＺＴＭ－Ａｌ_２Ｏ_３的性能和ＺｒＯ_２在瓷体中增韧机制的影响．发现Ｎｂ_２Ｏ_５的引入可明显提高瓷体中ｍ－ＺｒＯ_２含量而降低ｔ－ＺｒＯ_２含量,材料的机械性能也随Ｎｂ_２Ｏ_５添加量的增大出现了显著的改善,并且有韧性的平方正比于ｍ－ＺｒＯ_２含量的关系．ｍ－ＺｒＯ_２含量的增加强化了微裂纹增韧是材料性能改善的原因．     

Li2MnO3的柠檬酸盐溶胶-凝胶法合成及离子导电性

以Ｌｉ_２ＣＯ_３、ＭｎＣＯ_３为原料,用柠檬酸盐溶胶凝胶法合成了Ｌｉ_２ＭｎＯ_３超微粉．对合成的材料进行了ＤＴＡ、ＴＧ、ＸＲＤ和ＴＥＭ等表征,并应用交流阻抗谱技术测定了样品的电导率．结果表明,６５０。Ｃ以上生成Ｌｉ_２ＭｎＯ_３纯相超微粉,粒径在５０nｍ以下．在１８～４００℃温度范围内,产物烧结体的离子导电率为１０^－６～１０^－３Ｓ·ｃｍ^－１,其电导活化能为４４．８７ｋＪ·ｍｏｌ^－１．     

锂离子电池正极材料LiV3O8的低温合成研究

以ＬｉＮＯ_３和ＮＨ_４ＶＯ_３为原料,通过溶胶－凝胶法制备了层状锂钒氧化物ＬｉＶ_３Ｏ_８锂离子电池正极材料,通过ＴＧ－ＤＴＧ、ＸＲＤ等考察了合成条件对产物首次放电比容量的影响．实验结果表明,在４５０℃左右热分解２０ｈ可得到单一相产物ＬｉＶ_３Ｏ_８,其层状结构较为完整,电化学性能好,首次放电比容量可达３５０ｍＡｈ·ｇ－１,作为高能锂离子电池正极材料较为理想．     

磁场对KNbO3熔体中温度分布影响的实验研究

研究了磁场对ＫＮｂＯ_３熔体中的温度分布的影响．利用加磁场的休仑微分干涉显微实时观察装置及一种近似的间接测温方法,对在不同磁场强度０、７０、１１７、１３５ｍＴ下,ＫＮｂＯ_３熔体中的径向温度分布进行测量．发现随着磁场强度的增大,熔体中的径向温度梯度减小,尤其在坩埚－熔体界面附近,浮力驱动对流占主要作用的区域,温度梯度的减小更加明显．这可能是由于磁场对熔体中浮力驱动对流抑制的结果．     

纳米级LiMn2O4尖晶石合成及电化学性能研究

以Ｌｉ_２ＣＯ_３和Ｍｎ（ＮＯ_３）_２为原料,以聚丙烯酰胺为高分子网络剂制得前驱体后,用微波加热技术合成了纳米晶尖晶石ＬｉＭｎ_２Ｏ_４粉体,通过循环伏安及充放电技术对其进行电化学性能测试表明,该材料的电化学比容量为 １２０ｍＡｈ／ｇ;循环 ５０次后衰减率为 ４．７％;通过 ＳＥＭ及ＸＲＤ分析其微观形貌表明,该材料不仅相纯度高,而且颗粒粒度近于纳米级,有利于Ｌｉ^＋的嵌入／脱嵌．本文所提供的微波一高分子网络技术不仅为合成具有优良性能的锂锰尖晶石氧化物材料提供了一个新方法,而且为合成其他类型高性能氧化物陶瓷材料提供了一条新思路．     

NaOH-KOH熔盐中合成BaTiO3反应过程电导率的变化

用交流阻抗谱法测量了３５０℃时共晶成分的ＮａＯＨ－ＫＯＨ熔盐中加入ＴｉＯ_２和ＢａＣＯ₃时体系电导率的变化,准确给出了３５０℃共晶成分ＮａＯＨ－ＫＯＨ熔盐的电导率为１．０５３Ω－１·ｃｍ^－１,确认了在ＮａＯＨ－ＫＯＨ熔盐中ＴｉＯ_２与ＢａＣＯ_３反应,生成ＢａＴｉＯ_３时熔盐不参与反应．实验数据表明３５０℃ＴｉＯ_２与ＢａＣＯ_３在共晶成分的ＮａＯＨ－ＫＯＨ熔盐中的溶解过程可在短时间内达到平衡．     

PMN-PT弛豫铁电粉体的溶胶-凝胶法制备及其性质

以无机盐或氧化物Ｎｂ_２Ｏ_５、ＭｇＯ、ＴｉＣｌ_４和Ｐｂ（ＡＣ）_２、３Ｈ_２Ｏ为原材料,柠檬酸和ＥＤＴＡ为复合螫合剂,乙二醇为溶剂,分别制备Ｎｂ、Ｍｇ－Ｎｂ、Ｔｉ和Ｐｂ的有机化合物前驱液,采用溶胶－凝胶工艺制备ＰＭＮ－ＰＴ弛豫铁电陶瓷粉体及其烧结体．讨论了制备工艺和螯合剂等对金属有机化合物溶液的性质、材料物相形成和介电性能的影响．     

晶体生长三维实时观察技术研究

最近建立一套用干晶体三维实时观察的装置,主要分为光学观察部分,晶体生长部分,结果处理部分．采用二目观察法记录晶体生长和流体运动．设计并制造适于Ｂｒｉｄｇｍａｎ法晶体生长的生长炉和坩埚．初步观察到ＮａＮＯ_３晶体的固液界面形貌,并通过图像处理软件还原为三维真实图像．     

Evaluation of Morphology—Stable Critical Size of KNbO3 Crystals

Skeletal form of KnbO3 crystals growing in Li2B4O7 solvent was in-situ observed at 900℃ and it was found that shallow depression started to develop on the surface of KnbO3 crystals when the crystal size exceeded several micron,typically 7 micron.Based on the quantitative criterion derived by Chernov,the estimated critical size of KNbO3 crystals was 1 micron,which was consistent with the experimental measurement.The kinetic coefficients,Kcorner and Kcr,in the criterion were experimentally obtained in the diffusive-convective and diffusive-advective flow states respectively.     

熔体内重力对流速度场的实验研究及其理论分析

应用最近开发的高温光学实时观察法研究了铌酸钾熔体的重力对流现象．通过加热直径为2．5mm的圆环形坩埚,形成厚度为0．2mm的圆形KNbO₃熔液．实验测量了熔体内温度和流体速度的分布,并从理论上对速度场的分布给出了定量分析．     

Effects of convective fluid motion upon oxide crystal growth in high temperature solution

For understanding of the influence of convective flow on crystal growth, space high temperature in situ observation instrument (SHITISOI) is dedicated to visualize and record the whole growth process of oxide crystals in high temperature up to 1,000°C. Model experiments using transparent liquids such as KNbO₃ and a mixture of Li₂B₄O₇+KNbO₃ were chosen to investigate effects on ground and in space. On the earth, an investigation of growth kinetics of KNbO₃ crystal related to two different states of convection: diffusive-advective flow and diffusive-convective flow, has been performed. The per unit length of a step e is calculated from the experimental data for two different states of convection. Analyses of these data show the effect of buoyancy convection is to enhance the sharpness of the interface. The growth of KNbO₃ crystals from solution of KNbO₃+Li₂B₄O₇ was investigated in space. The streamlines of the steady thermocapillary convection in Li₂B₄O₇ solvent was observed. Due to thermocapillary convection, KNbO₃ crystal grains grew and filled the whole solution homogeneously. Earth-based quenching experiments are designed in order to study polyhedral instability of KNbO₃ crystal, which is controlled by diffusion mechanism limitation. In all cases, when the crystal was nucleated near air/solution surface, it lost its polyhedral stability and varied from polyhedrons to dendrites. The thickness of diffusion mechanism limitation layer is about 60 μm.     

Effects of convective fluid motion upon oxide crystal growth in high temperature solution

For understanding of the influence of convective flow on crystal growth, space high temperature in situ observation instrument (SHITISOI) is dedicated to visualize and record the whole growth process of oxide crystals in high temperature up to 1,000°C. Model experiments using transparent liquids such as KNbO₃ and a mixture of Li₂B₄O₇+KNbO₃ were chosen to investigate effects on ground and in space. On the earth, an investigation of growth kinetics of KNbO₃ crystal related to two different states of convection: diffusive-advective flow and diffusive-convective flow, has been performed. The per unit length of a step e is calculated from the experimental data for two different states of convection. Analyses of these data show the effect of buoyancy convection is to enhance the sharpness of the interface. The growth of KNbO₃ crystals from solution of KNbO₃+Li₂B₄O₇ was investigated in space. The streamlines of the steady thermocapillary convection in Li₂B₄O₇ solvent was observed. Due to thermocapillary convection, KNbO₃ crystal grains grew and filled the whole solution homogeneously. Earth-based quenching experiments are designed in order to study polyhedral instability of KNbO₃ crystal, which is controlled by diffusion mechanism limitation. In all cases, when the crystal was nucleated near air/solution surface, it lost its polyhedral stability and varied from polyhedrons to dendrites. The thickness of diffusion mechanism limitation layer is about 60 μm.     

Construction of Cuprous Oxide Electrodes Composed of 2D Single‐Crystalline Dendritic Nanosheets

An unusual anisotropic growth of Cu₂O is stabilized via the electrochemical synthesis of Cu₂O in the presence of Ag⁺ ions, which results in the formation of Cu₂O electrodes composed of 2D sheetlike crystals containing complex dendritic patterns. It is quite unusual for Cu₂O to form a 2D morphology since it has a 3D isotropic cubic crystal structure where the a, b, and c axes are equivalent. Each Cu₂O sheet is single‐crystalline in nature and is grown parallel to the {110} plane, which is rarely observed in Cu₂O crystal shapes. A various set of experiments are performed to understand the role of Ag⁺ ions on the 2D growth of Cu₂O. The results show that Ag⁺ ions are deposited as silver islands on already growing Cu₂O crystals and serve as nucleation sites for the new growth of Cu₂O crystals. As a result, the growth direction of the newly forming Cu₂O crystals is governed by the diffusion layer structure created by the pre‐existing Cu₂O crystals, which results in the formation of 2D dendritic patterns. The thin 2D crystal morphology can significantly increase the surface‐to‐volume ratio of Cu₂O crystals, which is beneficial for enhancing various electrochemical and photoelectrochemical properties of the electrodes. The photoelectrochemical properties of the Cu₂O electrodes composed of 2D dendritic crystals are investigated and compared to those of 3D dendritic crystals. This study provides a unique and effective route to maximize the {110} area per unit volume of Cu₂O, which will be beneficial for any catalytic/sensing abilities that can be anisotropically enhanced by the {110} planes of Cu₂O.     

溶质表面张力对流模型及其对空间实验的解析

空间高温实时观察装置（SHITISOI）被用于观察和记录在Li₂B₄O₇溶体中KNbO₃胞状结晶的整个生长过程,并对胞状结晶生长过程中浮力对流和表面张力对流的影响进行了研究．首次观察到空间条件下,Li₂B₄O₇溶体中稳态表面张力对流图像,它呈镜面对称的抛物线状．由于表面张力对流的作用,KNbO₃胞晶生长且充满了整个的溶体．而在地面上,由于浮力抑制表面张力,降低了胞晶在流体中的生长速度,使溶质KNbO₃胞晶在Li₂B₄O₇溶体中分布不均匀,本文还提出了胞状结晶生长理论的模型．这个模型的主要特点是表面张力对流起始于KNbO₃胞晶的界面上;这是由于KNbO₃溶质扩散速率减少而引起的KNbO₃溶质表面张力梯度．本模型的预言和实验所观察的现象吻合得比较好,这说明该理论模型是合理、可靠的．     

Influence of spinel substrate and over-layer for enhanced SAW and AO properties with KNbO3 thin film

Surface acoustic wave (SAW) propagation characteristics have been studied using modeling calculations for a potassium niobate (KNbO/sub 3/) thin film-layered structure with [001] and [110] orientation on a single crystal spinel (MgAl/sub 2/O/sub 4/) substrate, and a spinel buffer layer on silicon. Variation in the electromechanical coupling and acoustic attenuation has been compared. A significantly high value of coupling factor (k/sub max//sup 2/=23%) is obtained for the [001]KNbO/sub 3//spinel structure by introducing an optimum thickness of spinel over-layer for potential wide bandwidth SAW device applications. The dispersion characteristics with the [110] KNbO/sub 3/ orientation indicate an initial peak in the coupling coefficient value (k/sub max//sup 2/=8.8%) at a relatively low KNbO/sub 3/ film thickness that appears attractive for fabricating devices with thinner films. The KNbO/sub 3/ film with [001] orientation is found attractive for efficient acousto-optic (AO) device application with the formation of a symmetric waveguide structure (spinel(0.5 /spl mu/m)/KNbO/sub 3/(1.0 /spl mu/m)/spinel). A high value of k/sup 2/=23.5% with 50% diffraction efficiency has been obtained for the spinel(0.5 /spl mu/m)/KNbO/sub 3/(1.0 /spl mu/m)/spinel structure at 1 GHz SAW frequency and 633 nm optical wavelength at a very low input drive power of 15.4 mW.     

1Cr18Ni9Ti不锈钢双辊薄带凝固组织区的形成机理

在双辊薄带连铸实验和薄带凝固组织特征分析的基础上,结合对薄带凝固组织区的模拟预测结果,研究了1Cr18Ni9Ti不锈钢双辊薄带凝固组织区(特别是等轴晶区)的形成机理.结果表明:1Cr18Ni9Ti不锈钢双辊薄带凝固组织中的等轴晶区不但在凝固类型为半固态时形成,在轧制或理想型时也能形成.其形成机理为,熔池中悬浮游离晶体的沉积、聚集以及在枝晶生长前沿的长大和薄带离开二铸辊最小间隙(铸辊出口)后,薄带/空气界面换热系数骤然降低抑制了柱状枝晶的生长,并促使薄带中部未凝固熔体中游离晶体的择优长大.     

Kinetically controlled fabrication of C60 1-dimensional crystals

Considering the current application of fullerenes in the field of organic semiconductor devices, the highly crystalline or single crystal fullerene nanostructures with controlled shape and size contains some breakthrough for improved efficiency. Recently, fullerene 1-dimensional nanostructures, including nanowhiskers and nanotubes, become attractive kind of materials since the development of liquid-liquid interface precipitation (LLIP) process. The LLIP process has critical advantage; the fabrication of highly crystalline, even single crystal, fullerene 1-dimensional nanostructures with simple apparatus. However, the fabrication fullerene 1-dimensional structures by LLIP process requires long process time from one day to several days. In order to overcome this drawback, a modified process from conventional LLIP process is suggested. In the modified LLIP process, the nucleation step and growth step were divided. For the nucleation step, saturated fullerene solution is mixed with small amount of alcohols such as 2-propanol or ethanol. For the controlled growth step, the fullerenes in the nucleated solution are precipitated by addition of alcohol, which is injected to the bottom of the solution with controlled flow rate. In this modified process, the shape of the precipitated fullerene crystals is critically dependent on the nucleation steps and the size is dependent on the precipitation rate. By combination of proper nucleation step and growth rate, a well defined fullerene 1-dimensional structures, of 200-500 nm width and of hundreds microm length can be fabricated within two hours. In addition, by controlling injection rate and degree of supersaturation, several types of 1-dimensional structures including micro-tubes can be prepared and, by changing solvent and alcohol, several shape of C60 crystals including polyhedral particles and plates can be prepared.     

Interface effect on ferroelectricity at the nanoscale

Interfaces play a critical role in nanoscale ferroelectricity. We perform a first-principles study of ultrathin KNbO(3) ferroelectric films placed between two metal electrodes, either SrRuO(3) or Pt. We show that bonding at the ferroelectric-metal interfaces imposes severe constraints on the displacement of atoms, destroying the bulk tetragonal soft mode. If the interface bonding is sufficiently strong, the ground-state represents a ferroelectric domain with an interface domain wall, driven by the intrinsic oppositely oriented dipole moments at the two interfaces. The critical thickness for the net polarization of the KNbO(3) film is predicted to be about 1 nm for Pt and 1.8 nm for SrRuO(3) electrodes.