Acoustical study of the phase trawsition in SrTiO3 surface layers

Velocity and attenuation of surface and bulk acoustic waves were measured in SrTiO₃ in the phase transition region. The model of surface layer with thickness which does not vary with temperature is proposed. The layer transforms into the low-symmetry phase at temperature higher than the Curie temperature of the bulk. Effect of surface polishing on phase transition in the layer was observed.     

Combustion-synthesis of SrTiO3Part II. Sintering behaviour and surface characterization

Nanocrystalline powders of SrTiO₃ prepared via combustion-synthesis were sintered at 800 resp. 1000°C. The powders exhibited different grain growth velocities which were measured via X-ray diffraction (XRD). The existence of different SrCO₃-species was found by Fourier-transform infrared spectroscopy (FTIR). These could be assigned either to bulk- or surface-SrCO₃-species which could be proved by their different decomposition temperatures in thermogravimetry combined with mass spectrometry (TG/MS). A dependence between the grain growth velocities and the existence of surface-SrCO₃-species was found: samples which develop surface carbonate species for longer times during sintering will exhibit faster growth rates than samples which showed these species for shorter times. The surfaces of the crystallites are predominantly SrO-terminated which is in agreement with former results of other authors. The strong variations in sintering behaviour caused by only small differences between various samples are typical for nanocrystalline materials, they may be prepared by sol–gel or combustion-synthesis.     

Study on the Anti-Coking Nature of Ni/SrTiO3 Catalysts by the CH4 Pyrolysis

A solid phase crystallization (spc) method was applied for the preparation of SrTiO₃-supported Ni catalysts and compared to the impregnation (imp) method. spc-Ni_0.2/SrTiO₃ has highly dispersed and stable Ni metal particles resulting in higher activity and higher sustainability against coking than imp-Ni_0.2/SrTiO₃ in the partial oxidation of CH₄. Both catalysts were tested for the CH₄ pyrolysis in order to elucidate the catalytic nature against coking of spc-Ni_0.2/SrTiO₃. The amount of carbon and the rate of H₂ formation were similar over both catalysts at both 773 and 1073 K. On both catalysts, CH₄ continuously decomposed at 773 K, while the rate of CH₄ pyrolysis quickly decreased at 1073 K. Fibrous carbons grew up with a Ni metal particle on the tip of the fiber at 773 K, while carbon balls and short carbon fibers with a Ni metal particle encapsulated inside formed and no sufficient growth of the fiber was observed at 1073 K. The carbon species formed at 773 K was hydrogenated completely to CH₄ around 873 K, while the hydrogenation of that formed at 1073 K needed higher temperature around 1073 K. However, the carbon species formed on both the catalysts at either 773 or 1073 K was completely oxidized around 773 K. Thus, judging from the anti-coking nature, the behaviors in the CH₄ pyrolysis are similar over both catalysts, nonetheless spc-Ni_0.2/SrTiO₃ was far superior to imp-Ni_0.2/SrTiO₃ in the CH₄ oxidation. It is likely that the high sustainability against coking of spc-Ni_0.2/SrTiO₃ is not due to its intrinsic nature suppressing the coking but due to its high activity of reforming which can quickly eliminate the carbon formed on the catalyst surface.     

Control of epitaxial relationships of ZnO/SrTiO3 heterointerfaces by etching the substrate surface

In this work, the thermal expansion properties of carbon nanotube (CNT)-reinforced nanocomposites with CNT content ranging from 1 to 15 wt% were evaluated using a multi-scale numerical approach, in which the effects of two parameters, i.e., temperature and CNT content, were investigated extensively. For all CNT contents, the obtained results clearly revealed that within a wide low-temperature range (30°C ~ 62°C), thermal contraction is observed, while thermal expansion occurs in a high-temperature range (62°C ~ 120°C). It was found that at any specified CNT content, the thermal expansion properties vary with temperature - as temperature increases, the thermal expansion rate increases linearly. However, at a specified temperature, the absolute value of the thermal expansion rate decreases nonlinearly as the CNT content increases. Moreover, the results provided by the present multi-scale numerical model were in good agreement with those obtained from the corresponding theoretical analyses and experimental measurements in this work, which indicates that this multi-scale numerical approach provides a powerful tool to evaluate the thermal expansion properties of any type of CNT/polymer nanocomposites and therefore promotes the understanding on the thermal behaviors of CNT/polymer nanocomposites for their applications in temperature sensors, nanoelectronics devices, etc.     

Ce4+掺杂对SrTiO3光催化剂结构及性能的影响

用溶胶–凝胶法制备铈(Ce)掺杂改性钛酸锶(SrTiO3)光催化剂,采用X射线衍射仪、红外光谱仪、扫描电子显微镜、能谱仪、粒度分析仪检测了改性SrTiO3的结构及表面性能,并通过催化降解亚甲基蓝考察了该SrTiO3的光催化性能。研究表明:Ce4+替代SrTiO3的Sr2+,使催化剂表面的Ti4+含量减少,粒径减小,比表面积增大,提高光生电子和空穴的利用率。Ce4+改性SrTiO3催化剂表面吸附氧和吸附H2O含量增加,导致光催化活性中心增多。Ce4+的4f能级使SrTiO3形成新的能带,并且循环捕获光电子还原为Ce3+,延长光生电子和空穴的寿命,提高SrTiO3的催化活性。掺杂3%(摩尔分数)Ce4+的SrTiO3对亚甲基蓝的降解率可达98.7%。     

Detailed temperature dependence of the space charge layer width at grain boundaries in acceptor-doped SrTiO3-ceramics

The influence of temperature and the donor-type grain boundary (GB) states on the width of the space charge layer d_GB at GBs in SrTiO₃ ceramics was investigated by comparing numerical simulation results with experimental data. According to recent results for the potential barrier height at the GB, the temperature behaviour of d_GB can be divided into two different regimes. For lower temperatures, d_GB is independent of the temperature, for higher temperatures it decreases with rising temperature due to a change in the occupation of the electronic GB donor states. By decorating the GB with suitable dopants, the space charge layer width and its temperature dependence can be influenced. This is due to a change of the effective GB charge.     

Microstructure and dielectric properties of SrTiO3 ceramics by controlled growth of silica shells on SrTiO3 nanoparticles

SrTiO₃@SiO₂ nanopowder was synthesized via a core-shell nano-scale technique that is known as the Stöber process. The effect of the SiO₂ concentration on microstructure, dielectric response and energy storage properties of SrTiO₃@SiO₂ ceramics was investigated. Transmission electron microscopy (TEM) results confirmed the formation of core–shell nanostructures with controlled shell thicknesses between 2 nm and 13 nm. After increasing SiO₂, a secondary phase with Sr₂TiSi₂O₈ appeared due to inter-diffusion reactions between the SrTiO₃ core and SiO₂ shells during the sintering process. The results show that both breakdown strength and energy density improved apparently. The homogeneous coating of silica on ST cores is considered to dominate the contribution to improved breakdown strength. The composition for SrTiO₃ coated with 2.5 wt% SiO₂ shows the maximum energy storage density (1.2 J/cm³) and a breakdown strength of 310 kV/cm. The former is higher than for pure SrTiO₃ (0.19 J/cm³). Measurements of the dielectric performance indicate that the SrTiO₃@SiO₂ ceramics possess good bias stabilities compared to pure ST ceramics.     

受主掺杂对钛酸锶氧敏传感器的影响

简单介绍了汽车用氧传感器,总结Mg2+,Fe3+,Al3+,Li+,Ag+,Mn2+,Cu2+,Ni2+等受主离子掺杂对钛酸锶氧敏性能的影响.综合比较铁、镁掺杂钛酸锶效果较好.     

钛酸锶缺陷化学研究进展

综述了未掺杂及掺杂钛酸锶的缺陷、钛锶比的影响以及钛酸锶的缺陷化学热力学等方面的研究进展。     

SrTiO3薄膜制备技术研究进展

拥有众多优良性能的SrTiO3薄膜已经受到了人们的广泛关注.本文首先对SrTiO3薄膜的性质和应用进行了简单介绍,然后从物理和化学两大类方法着重对其现有制备技术及研究进展进行了全面的综述,文章最后对SrTiO3薄膜的制备及器件研究领域进行了展望.     

Effect of nanostructure on the thermal conductivity of La-doped SrTiO3 ceramics

A series of La-doped (10 at.%) SrTiO₃ ceramics with grain size ranging from 6 μm to 24 nm was prepared from nanocrystalline powders using high-pressure field assisted sintering (HP-FAST). A progressive reduction of thermal conductivity κ with decreasing grain size was observed. At room temperature, κ of the ceramic with grain size of 24 nm (1.2 W m⁻¹ K⁻¹) is one order of magnitude lower than that of undoped single crystals. The strong suppression of κ can be ascribed to (i) the high concentration of lattice defects, (ii) the increasing contribution of grain boundaries to phonon scattering when the grain size is decreased to the nanoscale and (iii) a moderate amount (10–15 vol.%) of nanopores. These results demonstrate that nanostructuration can be a successful strategy to attain a considerable reduction of κ in heavily doped bulk oxide ceramics. The low electrical conductivity of the La:SrTiO₃ nanoceramics represents a major obstacle for thermoelectric applications.     

稳定的SrTiO3陶瓷浆料的制备

本采用胶体“电空间稳定机制”，以PMAA-NH4为分散剂，以沉降高度作为衡量浆料稳定性的参数，研究了SrTiO3粉末的悬浮流变特性及分散剂PMAA-NH4加入量对SrTiO3浆料稳定性的影响。在最佳pH值和分散剂加入量条件下，制备了高固相含量（50vol%)，稳定性和分散性好的SrTiO2浆料。     

SrTiO3复合功能陶瓷的AC阻抗谱研究

本文采用一次烧成法制备出SrTiO3电容-压敏复合功能陶瓷,测试了样品的交流阻抗谱,确定了样品的等效电路,分析了不同氧化热处理条件下的晶粒和晶界电学特性.结果表明,SrTiO3复合功能陶瓷晶界存在多种受主态形态,氧化热处理过程中晶粒保持其半导体特性,晶界绝缘程度显著提高.     

烧成对钛酸锶压敏陶瓷电学性能的影响

本文研究了烧结助剂、烧结温度和烧结气氛对SrTiO3压敏陶瓷材料性能的影响。结果表明：在烧结过程中使用Al2O3和H2SiO3作烧结助剂比用Li2CO3和H2SiO3效果更好；在1420℃烧结的样品与1400℃及1440℃相比，具有较好的综合电性能；烧结过程中，除要保证还原性气氛外，还要有一定的氧分压。     

改性添加物对SrTiO3基高压电容器瓷料性能的影响

本文在魏敏敏等人研究工作的基础上,研究了SrTiO3基瓷介电容器瓷料犤(Sr1-xPbx)TiO3犦y·(Bi2O3·3TiO2)y的高压电容器性能,着重讨论了Bi2O3、MnCO3、稀土元素M2O3改性添加物对材料性能的影响,研制出介电常数εr约3100,Eb>13.5kV/mm,△C/C(25-85℃)<6%的高压电容器瓷料。     

纳米钛酸锶粉体的制备及光催化研究

以乙酸锶和钛酸丁酯为前驱物,采用溶胶-凝胶法在低温下合成了高纯、超细SrTiO3粉体。采用扫描电镜及紫外吸收等测试手段,对制备的SrTiO3粉体的基本特性进行了表征,并对其光催化特性进行了研究。结果表明:随着热处理温度的升高,粉体的紫外吸收峰出现红移现象;降解率随时间的增加而增加,但随着光催化反应时间的延长,降解活性有所降低;800℃下钛酸锶粉体的甲基橙脱色率可达到78%。     

SrTiO3压敏材料研究进展

SrTiO3压敏材料的非线性伏安特性和介电性能优良,具有吸收高频噪声、前沿快速上升噪声及自复位等功能,在吸收电感性负载开关浪涌电压、保护双向可控硅开关器件、旁路电容器、微电机等方面应用广泛.本文综述了SrTiO3压敏材料的导电机理、添加剂以及制备工艺等方面的研究现状,并对其进行了展望.     

4000m^3／h空分设备的调试

介绍了KDON-4000／4000型空分设备的应用情况，阐述了其系统流程及流程特点，并针对其调试过程中发现的问题进行了处理，调试成功后生产出合格的氧气。