Effects of Processing Conditions on the Dielectric Properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>

There have been a number of recent reports of anomalously large permittivities (ε _r ≈ 10⁴) in the material CaCu₃Ti₄O₁₂. The dielectric spectra is characterized by a large, relatively temperature independent permittivity near room temperature which exhibits a dielectric relaxation above 100 K. The crystal structure of CaCu₃Ti₄O₁₂ can be described as pseudo-perovskite with a cubic unit cell with a lattice constant of 7.391 Å. The ubiquitous occurrence of this dielectric behavior in ceramics, single crystals, and thin films suggests that the polarization is not related to a simple conducting grain/insulating grain boundary-type system. While the precise origin of the dielectric response is not entirely clear, in this work it is shown that processing conditions have a significant influence on the room temperature dielectric properties. Specifically, the permittivity and loss exhibit a strong dependence on the oxygen partial pressure and sintering time. In fact, studies of the effects of sintering time and supporting evidence from capacitance-voltage measurements conclusively show that there is no direct relationship between the permittivity and grain size, as is the case in classical boundary layer systems. Lastly, with aliovalent doping the room temperature dielectric properties can be optimized to provide a high permittivity (ε _r ～ 8,000) dielectric with relatively low loss (tan δ < 0.05 at 1 kHz).     

智能电网地区继电保护定值整定系统关键技术研究

从智能电网发展的角度,分析了当前地区继电保护定值整定管理的网络拓扑、参数维护及定值与装置管理等相关问题,提出了智能电网条件下地区级继电保护整定系统总体设计结构.阐述了该智能整定系统的组成,其中包括整定计算、定值管理及保护重构三部分.同时论述了该系统的网络拓扑、供电方案、自动解环、分界拼接、自动整定、供电组合和继保重构等关键技术.该系统的设计思路能够有效地满足地区级智能电网保护整定系统的管理及技术要求.     

Electrical properties and Mössbauer spectra of rutile-type Fe1−x Mn x TiTaO6 (0 ≤ x ≤ 0.3) ceramics

Several electrical quantities of rutile-type Fe_1?x Mn _x TiTaO₆ (0 ≤ x ≤ 0.3) ceramics were measured between room temperature and ～ 770 K. One aim of the investigation was to study differences to data known from rutile-type FeTiTaO₆ ceramics, showing giant relaxor ferroelectric-type constant ??(ω) (ω is angular frequency). FeTiTaO₆ (x = 0) samples showed, as expected, capacitance C _p (ω) peaks at 500–600 K using Ag-paint contacts, however upon application of Pt-paint, C _p (ω) increased steadily up to the maximum employed temperature of ～ 770 K. For x = 0.02 (Ag-paint), C _p (ω) peaks were detected pointing to relaxor ferroelectric behaviour. For x > 0.02 (Ag-paint), no C _p (ω) peaks were observed; C _p (ω) increased for all frequencies steadily with temperature up to maximum values at the highest applied temperature. Complex plane impedance plots were characterized for each composition by two semicircular arcs due to bulk and grain boundary charge processes. A marked separation of arcs was observed for FeTiTaO₆ (x = 0) and 0.02; for x ≥ 0.05 this fact became much reduced. The derived DC conductivity σ _DC for bulk conduction showed Arrhenius behaviour for all compositions with activation energy E _A ～ 0.4–0.7 eV and σ _DC (300 K) ～ 10^?9 ? 10^?6Ω^?1cm^?1 depending on x. For x ～ 0.05, the frequency dependence of AC conductivity σ _AC (ω) was weak at and above room temperature, in contrast for x < or > 0.05 a distinct dispersion was measured showing in part UDR-type power law dependence. ⁵⁷Fe Mössbauer spectra consisted of one experimental doublet due to Fe³⁺; each spectrum could be adequately fitted using one doublet with Lorentzian line shape; there was enhanced line width for x = 0.05, pointing to atomic or nanoscale inhomogeneity.