The synthesis and properties of CaCu3Ti4O12 thin films

The CaCu₃Ti₄O₁₂ (CCTO) thin films were synthesized via a metal‐organic solution containing stoichiometric amounts of the metal cations at 700 °C for 1 h. The stable metal‐organic solution was prepared by dissolving calcium nitrate, copper nitrate, and tetrabuty titanate in grain alcohol. The phases, microstructures, and electric properties of CCTO thin films were characterized by X‐ray diffraction, scanning electron microscopy, atomic force microscope, and electric measurements. The results show that the CCTO thin films have homogeneous microstructure, smooth surface, low leakage current, and high values of dielectric constant. The low leakage current can be attributed to the small surface roughness. The high value of dielectric constant can be attributed to the internal barrier layer capacitor mechanism and metal‐insulator‐semiconductor junction of CCTO thin films. Copyright © 2013 John Wiley & Sons, Ltd.     

CaCu3Ti4O12 陶瓷介电模量响应特性的研究

由于CaCu₃Ti₄O₁₂巨介电常数陶瓷的低频区直流电导较大, 本文采用模量 M"-f频谱表征与分析了低频和高频的两个松弛极化过程. 研究认为, 这两个特征峰属于晶界区Schottky 势垒耗尽层边缘深陷阱的电子松弛过程, 其中高频松弛峰起源于晶粒本征缺陷的电子松弛过程, 而低频松弛峰则为与氧空位有关的松弛极化过程. 对于CaCu₃Ti₄O₁₂这类低频下具有高直流电导的陶瓷材料, 采用模量频谱能更有效地分析研究其损耗极化机理. 关键词： 3Ti₄O₁₂陶瓷')" href="#">CaCu₃Ti₄O₁₂陶瓷 模量 松弛过程 电导     

Soft chemistry synthesis of the perovskite CaCu3Ti4O12

The perovskite CaCu₃Ti₄O₁₂ (CCT) has been obtained after calcination of oxalate precursors at 900–1000 °C in air. Those precursors are prepared using a soft chemistry method, the coprecipitation. The oxalate powders consist of disk-like particles of 2–3 μm diameter and 300–400 nm thickness. By varying the ratio of the initial amounts of metal chlorides, additional phases (CaTiO₃, TiO₂ and CuO) could be obtained besides CCT. The corresponding multiphased ceramics present improved dielectric properties.     

Performance at 10–50 K of Bi-2212/Ag multilayer tape fabricated by using pre-annealing and intermediate rolling process

High-transport critical current density (J_c-oxide)>500 kA/cm² at 4.2 K, 10 T can be obtained for Bi-2212/Ag tapes fabricated by using pre-annealing and intermediate rolling (PAIR) and melt-solidification process. In this paper, we report high-temperature properties of PAIR-processed Bi-2212/Ag multilayer tape in order to show their potential for practical applications operated at cryocooling temperatures. Magnetic field dependence and angular dependence of critical current (I_c) are investigated at temperatures ranging 10–50 K by using helium gas cooling and liquid neon. Field-temperature curves for I_c=0.2 and 2.0 A are also determined in order to show the approximation of the irreversible field. High-temperature performance of the tape is attractive to consider future applications. For example, the best sample carries I_c=267 A (engineering-J_c=303 A/mm², J_c-oxide=151 kA/cm²) and 92 A (104 A/mm², 52 kA/cm²) at 27.1 K (in liquid neon), in magnetic fields (parallel to the tape surface) of 2 and 10 T, respectively. Engineering-J_c of 100 A/mm² is obtained even in the perpendicular field of 0.5 T at 27.1 K.     

La3+掺杂Ca1-xLaxCu3Ti4O12陶瓷的制备及性能研究

采用固相反应法制备了La3+掺杂的CaCu3Ti4O12(CCTO)陶瓷,研究了La3+掺杂量对Ca1-xLaxCu3Ti4O12(x=0;,1;,3;,5;,7;)陶瓷物相结构、微观形貌和介电性能影响,对La3+掺杂影响CCTO陶瓷介电性能的机理进行了分析.结果表明:x为3;时,开始出现杂相;x高于5;时,陶瓷晶粒开始细化;La3+掺杂可以显著提高CaCu3Ti4O12陶瓷的介电常数,同时介电损耗在高频段也相应降低,从而有助于CCTO陶瓷的综合介电性能的提升.     

Micro‐Raman study of exfoliated Bi2Sr2CaCu2O8+δ single crystals with different thicknesses

Exfoliated Bi₂Sr₂CaCu₂O_8+δ (Bi‐2212) single crystals were prepared by micromechanical cleavage of bulk Bi‐2212 single crystals on SiO₂/Si substrates. Room temperature micro‐Raman spectra were collected using a 532‐nm laser source. The evolutions of the spectra of A_1g (Bi), A_1g (Sr), and A_1g (O_Bi) Raman modes with different thicknesses of the samples were studied. The refractive index of Bi‐2212 single crystal was obtained by studying the intensity evolutions based on the interference effect. The observed wavenumber shifts of the A_1g (Bi), A_1g (Sr), and A_1g (O_Bi) modes were analyzed. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparison of the Efficiency of the One and Two-Step Process for the Production of BSCCO (2212) Powders by Means of Analytical Techniques

 The efficiency of the production of the high temperature superconducting powders Bi₂Sr₂CaCu₂O_8+x (BSCCO 2212) using the solid state reaction in one or two step processes under different thermal treatment was compared by means of different modern analytical techniques. Through the same techniques the optimization of the production of the production of Bi-2212 powder produced by the two step process, was achieved. X-ray diffraction analysis (XRD) and Raman spectroscopy were used to characterize the products for their stoichiometry and phase-purity. The grain size of the powders was observed by scanning electron microscopy (SEM), while their superconducting properties were tested by electrical DC-resistivity and magnetic susceptibility measurements using a superconducting quantum interference device (SQUID). It resulted that the two step process gives a high quality BSCCO 2212 superconducting powder with T _c = 85 K, in a shorter time and with a greater recovery rate than the one step process. Received May 3, 1999. Revision April 27, 2000.     

基于低温光声光谱技术的高Tc超导材料Bi2Sr2CaCu2O8

在光声光谱技术基础上,将不同仪器组装成一套系统,并成功测量出碳黑的光声光谱。利用低温检测系统测定高温超导材料Bi2Sr2CaCu2O8在室温和液氮温度下的光声光谱,发现室温时在598nm和695nm有峰值,液氮温度时在466nm出现峰值。以吸收系数近似为1的碳黑为参照,利用归一化方法得到了Bi2Sr2CaCu2O8相对吸收系数谱图,并进行了初步的探讨,得到了该超导材料的一些信息,为利用低温光声光谱技术,研究超导材料的超导特性提供了一种可行的途径。     

直流老化对CaCu3Ti4O12陶瓷介电性能的影响

在电场为3.5 kV/cm的条件下, 对CaCu₃Ti₄O₁₂陶瓷进行了60 h的直流老化, 研究了老化过程对CaCu₃Ti₄O₁₂陶瓷介电性能和电气特性的影响. J-E特性测试结果表明, 直流老化导致CaCu₃Ti₄O₁₂陶瓷击穿场强、非线性系数和势垒高度明显降低. 介电性能测试结果表明, 低频介电常数和介电损耗明显增大, 并且介电损耗随频率的变化遵从Debye弛豫理论, 可分解为直流电导损耗和弛豫损耗, 直流老化主要导致了电导损耗的增加. 在低温233 K, 介电损耗谱中出现两个弛豫峰, 其活化能分别为0.10, 0.50 eV, 认为对应着晶粒和畴界的弛豫过程, 且不随直流老化而变化. 通过电模量谱对CaCu₃Ti₄O₁₂陶瓷的弛豫过程进行了表征, 发现直流老化导致的界面空间电荷在外施交变电场的作用下符合Maxwell-Wagner极化效应, 并在低频区形成新的弛豫峰. 在高温323-473 K的阻抗谱中, 晶界弛豫峰在直流老化后明显向高频移动, 其对应的活化能从1.23 eV 下降到0.72 eV, 晶界阻抗值下降了约两个数量级. 最后, 建立了CaCu₃Ti₄O₁₂陶瓷的阻容电路模型, 分析了介电弛豫过程与电性能之间的关联.     

CaCu3Ti4O12陶瓷的介电特性与弛豫机理

本文采用Novocontrol宽频介电谱仪在-100 ℃–100 ℃温 度范围内、0.1 Hz–10 MHz频率范围内测量了表面层打磨前 后CaCu₃Ti₄O₁₂陶瓷的介电特性, 分析了CaCu₃Ti₄O₁₂陶瓷的介电弛豫机理. 首先, 基于对宏观“壳-心”结构的定量分析, 排除了巨介电常数起源于表面层效应的可能性; 其次, 基于经典Maxwell-Wagner夹层极化及其活化能物理本质的分析, 排除了巨介电常数起源于经典Maxwell-Wagner极化的可能性; 最后, 依据晶界Schottky势垒与本征点缺陷的本质联系, 提出了巨介电常数起源于Schottky势垒边界陷阱电子弛豫的新机理. 陷阱电子弛豫机理反映了CaCu₃Ti₄O₁₂陶瓷本征点缺陷、 电导、介电常数之间的本质关系. 关键词： 3Ti₄O₁₂')" href="#">CaCu₃Ti₄O₁₂ 介电弛豫 Schottky势垒 点缺陷