阻挡层电容对ACu3Ti4O12巨介电性能的影响研究

用固相反应法成功地制备了ACu3Ti4O12(A=Ca，La，Y)系列陶瓷，在50—300K温区内测量了样品的介电性能，分析了交流电导与外场频率、温度的关系.发现在相同组分的CaCu3Ti4O12晶体中相对含量大于等于0776时，样品的相对介电常数可达104；而A位上价态为3+的化合物La2/3Cu3Ti4O12和Y2/3Cu3Ti4O12相对介电常数仅为103.分析表明，样品中内部阻挡层电容数目的多少直接对ACu3Ti4O12的相对介电常数产生影响.电导与温度及频率的关系是由电子、声子与外场的共同作用决定的. 关键词： ACu3Ti4O12 巨介电 晶相含量 阻挡层电容     

CaCu3Ti4O12块材和薄膜的巨介电常数

用固相反应法和脉冲激光沉积 (PLD)制备了CaCu3Ti4O1 2 块材和薄膜 ,获得了相对介电常数ε′( 1kHz ,3 0 0K)高于140 0 0的介电特性 ,是目前该体系最好的结果 .报道了 ( 0 0l)取向高质量CaCu3Ti4O1 2 外延薄膜及其介电性质 .CaCu3Ti4O1 2 相对介电常数ε′在 10 0— 3 0 0K温度范围内基本保持恒定 ,稳定性好 .基于跳跃电导模型 ,对CaCu3Ti4O1 2薄膜介电电导的频率依赖关系作了合理解释     

添加Nb对CaCu3Ti4O12陶瓷介电性能的影响

采用固相反应法制备了CaCu3Ti4-xNbxO12(x=0,0.01,0.04,0.08,0.2)陶瓷,样品在x取值范围内形成了连续固溶体.在40 Hz-110 MHz频率范围对样品进行了介电频谱分析,实验结果表明,与纯CaCu3Ti4O12不同,含Nb试样除了在频率大于10 kHz范围内出现的德拜弛豫行为外,室温下在40 Hz-10 kHz低频率范围内还存在一个新的德拜弛豫峰,低于该弛豫特征频率时介电常数达106以上,该峰的特征频率随着Nb含量的增大向高频方向移动.根据阻抗谱中观察到的三个半圆弧,采用阻挡层电容模型,利用含有三个RC的等效电路对上述实验现象作了合理解释.     

La掺杂对Bi4Ti3O12薄膜铁电性能的影响

利用Sol-Gel法在Pt/Ti/SiO2/Si衬底上制备出Bi4Ti3O12和Bi3.25La0.75Ti3O12薄膜,研究了La掺杂对Bi4Ti3O12薄膜的晶体结构、铁电性能和疲劳特性的影响,发现La掺杂没有改变Bi4Ti3O12薄膜的基本晶体结构,并且提高了Bi4Ti3O12铁电薄膜的剩余极化值和抗疲劳性能,对La掺杂改善Bi4Ti3O12铁电薄膜性能的机理进行了讨论.     

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.     

磁控溅射法制备的CaCu3Ti4O12薄膜

采用溅射方法成功地制备了CaCu3Ti4O12薄膜,用原子力显微镜、x射线衍射(XRD)仪和LCR分析仪对样品进行形貌、物相结构和介电性质的研究.XRD表明,薄膜比块体的晶格常数小但晶格畸变较大;LCR测量结果显示,在相同温度下薄膜比块体的相对介电常数低,薄膜相对介电常数由低到高转变时对应的温度较高且激活能较大.分析表明:薄膜的相对介电常数较低是样品中晶相含量较低、缺陷较多使内部阻挡层电容大量减小、致密度不高引起的;薄膜中激活能的增大由膜和基底间晶格的不匹配造成膜中的内应力增大、微结构、缺陷和畴等因素决定;介电常数在低频时的急剧增大,意味着存在界面极化,它与界面的缺陷、悬挂键有关.     

Bi4-xLax Ti3O12-SrBi4-y Lay Ti4O15共生结构铁电材料拉曼光谱研究

在常温下 ,对La掺杂共生结构铁电陶瓷Bi4 -xLaxTi3O1 2 _SrBi4 -yLayTi4 O1 5[BLT_SBLT(x y) ,x y =0 0 0 ,0 2 5 ,0 5 0 ,0 75 ,1 0 0 ,1 2 5 ,1 5 0 ]进行了拉曼光谱研究 .结果表明 ,在掺杂量低于 0 5 0时 ,La只取代类钙钛矿层中的Bi,当掺杂量高于 0 5 0后 ,部分La开始进入 (Bi2 O2 ) 2 层 .La取代 (Bi2 O2 ) 2 层中的部分Bi以后 ,(Bi2 O2 ) 2 层结构发生变化 ,原有的绝缘层和空间电荷库的作用减弱 ,导致材料剩余极化下降 .La掺杂量增至 1 5 0时 ,样品出现弛豫铁电性 ,这与 30cm- 1 以下模的软化相对应 ,说明La掺杂可引起材料的结构相变     

巨介电常数氧化物CaCu3Ti4O12的介电和阻抗特性

采用固相烧结法合成了单相巨介电常数氧化物CaCu₃Ti₄O₁₂（CCTO）.用阻抗分析仪分析了10—420 K温度范围内的介电频谱和阻抗谱特性,并结合ZVIEW软件进行了模拟.结果表明：温度高于室温时,频谱出现两个明显的弛豫台阶,低频弛豫介电常数随温度升高而显著增大,表现出热离子极化特点;温度低于室温时,频谱表现出类德拜弛豫,且高、低平台介电常数值基本不随温度变化,表现出界面极化特点和较好的温度稳定性.频谱中依次出现的介电弛豫对应于阻抗谱中 关键词： 3Ti₄O₁₂')" href="#">CaCu₃Ti₄O₁₂ 介电频谱 阻抗谱 Cole-Cole半圆弧     

CaCu3Ti4O12块材和薄膜的巨介电常数

用固相反应法和脉冲激光沉积(PLD)制备了CaCu₃Ti₄O₁₂块材和薄膜，获得了相对介电常数ε′（1kHz,300K)高于14000的介电特性，是目前该体系最好的结果.报道了(00l)取向高质量CaCu₃Ti₄O₁₂外延薄膜及其介电性质.C aCu₃Ti₄O₁₂相对介电常数ε′在100—300K温度范围 内 关键词： 3Ti₄O₁₂')" href="#">CaCu₃Ti₄O₁₂ 巨介电常数 PLD     

Analysis of Electrical Properties of Post-Annealed Polycrystalline CaCu3Ti4O12 Films by Impedance Spectroscopy

Impedance spectroscopy is performed to establish the electrical property and microstructure relations of the asdeposited and post-annealed polycrystalline CaCu3Ti4O12 （CCTO） films. Our results show that the resistance and capacitance of the grains and grain boundaries could be tuned by changing the annealing atmosphere and temperature. The simple resistor-capacitor equivalent circuit and the modified constant phase element （CPE） circuit are used to describe the impedance spectroscopy, and excellent agreement between the calculated and measured curves is obtained in the CPE circuit. Based on the experimental results, it is suggested that the origin of the semiconductivity of the grains in CCTO polycrystalline films originates from their oxygen-loss, while the grain boundaries are close to oxygen- stoichiometry.     

Enhanced giant dielectric response in Mg-substituted CaCu3Ti4O12 ceramics

Effects of Mg-substitution on the giant dielectric response in CaCu₃Ti₄O₁₂ ceramics were investigated and discussed. A significantly enhanced giant dielectric response was obtained in Ca(Cu_1?xMg_x)₃Ti₄O₁₂ ceramics, and the dielectric constant step increased with increasing Mg-substitution content. The results of X-ray photoelectron analysis confirmed the obvious increase of Ti³⁺/Ti⁴⁺ ratio, and the enhanced giant dielectric response should originate from the corresponding modification of the mixed-valent structure. The present results have great scientific significance in deepening the understanding on the origin of giant dielectric response and modulating the giant dielectric constant step in CaCu₃Ti₄O₁₂.     

Dc-bias-field-induced dielectric relaxation and ac conduction in CaCu3Ti4O12 ceramics

The dielectric relaxation and ac conduction of CaCu₃Ti₄O₁₂ (CCTO) ceramics were investigated at different temperatures under a dc bias. The dc bias gives rise to space charge accumulation, i.e. an electrode response, resulting in the significant increase of dielectric permittivity and dielectric loss tangent. Two Debye-like relaxations, arising from electrode and grain boundary responses, are present at low frequency with an increase of the dc bias. The electrode and grain boundary relaxations are distinguished according to the impedance spectroscopy and the frequency-dependent ac conductivity. The relaxation times of electrode and grain boundary relaxation are 0.955 ms and 0.026 ms, respectively, with a dc bias of 10 V at 328 K.     

Enhanced multiferroic characteristics in Fe-doped Bi4Ti3O12 ceramics

Modification of Bi₄Ti₃O₁₂ multiferroic ceramics prepared by a conventional solid state reaction method were investigated by substituting Ti partly with Fe. The introduction of Fe does not change the layered perovskite structure of Bi₄Ti₃O₁₂. Upon increasing Fe content, the remnant polarization of the samples is enhanced. The magnetism of the ceramics at room temperature develops from diamagnetism to weak ferromagnetism with increasing Fe doping. The largest variations of 15% and 6% in remnant polarization and magnetization, achieved in a Bi₄Ti₁Fe₂O_12?δ sample after poling it in a magnetic field at 1 T and a DC electric field at 30 kV/cm for 10 min, are evidence of magnetoelectric coupling between the electric dipoles and magnetic dipoles at room temperature. The present results suggest a new candidate for a room temperature multiferroic material with enhanced properties.     

Enhanced dielectric and nonohmic properties of SrTiO3-modified CaCu3Ti4O12 ceramics

Dielectric and nonohmic properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics can be modified by addition of SrTiO₃ (STO) in different molar proportions which were fabricated by a modified sol-gel method. XRD results indicated that all modified ceramics showed mixed phase consisting of both CCTO and STO. SEM images and grain size distribution probability also presented the change of microstructure with the addition of STO. The dielectric loss of the CCTO/0.4STO ceramics sintered at 1000 °C can be lower than 0.02 in a wide frequency (1 kHz–10 kHz), especially at 1 kHz, the dielectric loss of this sample is as low as 0.012. Furthermore, excellent nonlinear I–V electrical characteristic (high breakdown voltage to 54.15 kV/cm for CCTO/0.4STO sintered at 1000 °C) was observed as well. All the results indicated that the addition of STO does improve the dielectric properties and nonohmic characteristics of CCTO ceramics dramatically.     

EELS characterisation of bulk CaCu3Ti4O12 ceramics

CaCu3Ti4O12 (CCTO) is a cubic perovskite phase and sintered ceramics exhibit high permittivity at room temperature. Electron energy-loss spectroscopy (EELS) and energy dispersive X-ray spectrometry (EDS) data have been collected from samples of CCTO to relate the observed electrical properties to the microstructure and chemistry on the nanoscale. CCTO ceramics were sintered for 24h at 1115 degrees C in air, giving a grain size of 50-300 microm. Ti L(2,3)-, Cu L(2,3)- and O K-edge EEL data were collected for bulk CCTO (within grain) and compared with well characterised Ti-oxides, CaTiO3 and BaTiO3 perovskites. The bulk metal L(2,3)-edge data for CCTO suggest that Cu is divalent and Ti is present as Ti4+. The O K-edge of CCTO shows increased near-edge structure (NES) compared to those of the simple perovskites.     

Investigation of the thermal expansion and heat capacity of the CaCu3Ti4O12 ceramics

The thermal expansion of the CaCu₃Ti₄O₁₂ ceramics has been measured over a wide temperature range 120?C1200 K. The high quality of the samples under study has been confirmed by good agreement of the results of measurements of the heat capacity in the range 2?C300 K and in the vicinity of the phase transition of magnetic nature at 25 K with the data for the single crystal. No anomalies in the thermal expansion that can be associated with the phase transition at 726?C732 K assumed by other investigators have been found. The influence exerted on the thermal expansion by the heat treatment of the sample in a helium atmosphere and in air has been investigated.