Surface Structure of Oxygen Annealed Donor Doped SrTiO3(100) Single Crystals Studied with Spectroscopic Electron Microscopy

Heating 5at.% (on A-site) La-doped SrTiO₃(100) single crystals in an ambient atmosphere at 1300°C for 120 h results in the formation of insulating islands on top of the surface with typical dimensions of up to 50 m. The islands and the surface between them were investigated by spectroscopic Metastable Impact Electron Emission Microscopy (specMIEEM) and Photoelectron Emission Microscopy in order to determine its electronic and geometric structure.The comparison of specMIEEM results with MIES (Metastable Impact Electron Spectroscopy) spectra from stoichiometric SrO shows that the insulating islands, which most likely consist of SrO, are at least partly covered by another species, probably SrO₂. All these islands are surrounded by 2–3 m wide haloes. The electronic structure of these haloes is quite different from that of SrO and SrTiO₃ but similar to the electronic structure of TiO₂ or Ti₂O₃. It is suggested that the depletion of SrO from Ruddlesden-Popper (Sr _{n + 1}Ti _n O_{3n + 1}) phases results in the formation of SrO islands.     

A Mathematical-Physical Model for the Charge Transport in p-Type SrTiO3 Ceramics Under dc Load: Maxwell-Wagner Relaxation

A mathematical-physical model to describe the current response of p-type SrTiO₃ ceramics in the low-temperature regime upon dc voltage step was developed, utilizing the numerical class library DIFFPACK (Numerical Objects, Norway). The current response in the time domain shows the experimentally observed Maxwell-Wagner relaxation (space charge polarization), followed by leakage current, and, eventually, resistance degradation. The relaxation behavior is analyzed by means of the simulation results for the spatial profiles of the electrical potential and the respective point defects. The impact of bias voltage and grain boundaries on the relaxation time is investigated. The simulation results are compared with experimental data.     

The Influence of Laterally Inhomogeneous Contacts on the Impedance of Solid Materials: A Three-Dimensional Finite-Element Study

The total impedance of samples with electrodes exhibiting only partial contact (porous electrodes) is investigated using the finite element method in three dimensions. Emphasis is put on porous electrodes built up of arrays of small perfect contacts. An equivalent circuit to analyze the impedance spectra is put on a firm basis enabling the reliable determination of bulk properties of imperfectly contacted samples. Approximations are given to estimate the contact geometry impedance. The results are also applicable to other imperfect contact problems as occurring at grain boundaries.     

测量仪器输入阻抗对断路器分合闸速度的影响

进行断路器的型式试验时,国家标准要求测量断路器的机械特性,一般利用滑动电阻器测量断路器分、合闸速度。通过对测量设备的输入阻抗对测量精度影响的讨论分析,明确了输入阻抗与测量精度的关系,有利于测量时设备的正确选择,保证测量结果的准确性。     

基于阻抗分析法研究光伏并网逆变器与电网的动态交互影响

大量存在的并网逆变器会对分布式发电系统的电能质量和系统稳定性造成深刻影响,该文基于阻抗分析方法研究光伏并网逆变器与电网间的交互影响。论文定量分析光伏并网逆变器与电网之间由于阻抗交互影响所产生的谐波振荡,并通过基于硬件在环的分布式发电综合实验平台验证不同电网接入条件对并网逆变器稳定性的影响;推导LCL型并网逆变器的系统阻抗模型,并提出一种基于电压前馈的主动阻抗控制策略来提高逆变器与电网之间的稳定相角裕度,使光伏并网逆变器在不同的动态电网条件下均具有较好的控制鲁棒性;最后给出阻抗主动调整控制策略的设计过程和参数设计方法,并通过仿真验证主动阻抗控制策略的有效性。     

惰性载体Al_2O_3对Fe_2O_3及CuO氧载体煤化学链燃烧的影响

氧载体是煤化学链燃烧技术的基础,惰性载体则是其中的必要组成部分,起着重要的作用。以Al2O3作为典型惰性载体,采用热重分析仪、红外频谱仪、场发射扫描电镜和能谱分析仪以及X衍射仪,对六盘水贫煤与Fe2O3、CuO基氧载体的反应进行了详细的研究。研究发现,Al2O3的引入,使得Fe2O3、CuO基氧载体表面积增大、孔径分布更为优化,而且对氧载体与六盘水贫煤一次热解产物的反应是有利的,能够促进氧载体中更多晶格氧的传递,Fe2O3基氧载体中有更多的Fe2O3还原为低于Fe3O4价态的氧化物,而CuO基氧载体中CuO除了还原为Cu、Cu2O外,其中的CuAl2O4也有一定的反应活性,被还原为CuAlO2。与LPS煤反应时,Fe2O3深度还原产物与部分Al2O3及煤中的SiO2反应生成Fe3Al2（SiO4）3,而CuO则与Al2O3及六盘水贫煤反应生成了（Cu0.215Mg1.785）（Al4Si5O18）复合物。     

高氧浓度下大气压Ar/O_2脉冲介质阻挡放电频率特性数值研究

使用一维流体模型,研究了高氧浓度(1.0%~5.0%)下大气压Ar/O_2脉冲介质阻挡放电的频率(100k Hz)效应。在所考虑的氧浓度和频率范围内,计算了放电电流密度以及四种(O、O(~1D)、O~2(~1Δg)、O_3)活性氧粒子产生与消耗的主要路径及其贡献随频率的变化。结果表明,一个电压脉冲周期中均发生两次极性相反的放电,并分别发生在外施电压脉冲的上升沿和下降沿。不同氧浓度下,第一次放电与第二次放电的放电电流密度峰值均随着频率的增加先减小后增大,即存在最小值,相应的频率定义为特征频率,并获得了二特征频率随氧浓度的变化。另外,在氧浓度为3.0%时,给出了四种活性氧粒子产生与消耗的主要路径及其在不同频率下相应的贡献。