CaCu_3Ti_4O_(12)陶瓷的巨介电响应机理

针对CaCu3Ti4O12(CCTO)陶瓷的巨介电性起源存在较大争议的情况,以少量MnO2取代CCTO中CuO或TiO2、采用固相反应法烧结制备名义成分为CaCu3-xMnxTi4O12(x=0~0.3)和CaCu3Ti4-yMnyO12(y=0~0.1)的陶瓷。通过微结构和电性能的演变讨论CCTO陶瓷的巨介电响应机理。结果表明:加入少量MnO2后,所有陶瓷均为体心立方(BCC)类钙钛矿结构的CCTO单相;但是,CCTO陶瓷显微结构从异常长大的晶粒转变成均匀的细小晶粒;同时,CCTO陶瓷的电阻率从107-.cm显著提高到109-.cm;介电常数从104显著下降到102;介电损耗从10-1急剧降低到10-3;CCTO陶瓷的巨介电响应是由半导体化的晶界/亚晶界和相对绝缘的晶粒/亚晶粒组成的内部阻挡层电容器(IBLC)所致。在较低温度下(<1 100℃)烧结获得高介电常数、低损耗和温度稳定的CCTO基陶瓷,找到一种降低CCTO陶瓷介电损耗的有效方法。     

预烧温度对CaCu3Ti4O12陶瓷结构和介电性能的影响

采用固相反应法在不同温度（950～1100℃）下预烧后烧结制备CaCu3Ti4O12（CCTO）陶瓷。对CCTO陶瓷进行物相分析，并测试了20Hz-1MHz频率范围和25～150℃温度区间的介电性能和阻抗谱，详细研究了预烧温度对CCTO陶瓷烧结性能、晶体结构和介电性能的影响。结果表明，较低的预烧温度有利于CCTO陶瓷的烧结，容易获得介电性能较好的CCTO陶瓷。950℃预烧后，于1120℃烧结的CCTO陶瓷室温1kHz频率下介电常数可达12444。     

ZnO-B_2O_3对CaCu_3Ti_4O_(12)陶瓷结构和介电性能的影响

采用传统固相反应法,将ZnO-B2O3(ZB)与1 100℃预烧的CaCu3Ti4O12(CCTO)粉末混合烧结成陶瓷。探讨ZB对CCTO陶瓷显微结构和介电性能的影响,并进一步分析CCTO陶瓷的巨介电机理。结果表明:当添加少量ZB(w≤2%,质量分数)时,形成体心立方BCC类钙钛矿结构的CCTO单相;当w>2%时,生成Zn2TiO4杂相;当ZB的添加量为0.5%和10%时,CCTO陶瓷的介电常数明显增大,介电损耗也较高;而当ZB的添加量为1.0%~5.0%时,介电常数的变化很小,同时具有较低的损耗和良好的温度稳定性。其中,w=2%时CCTO基陶瓷具有优异的介电性能(100 kHz),即相对介电常数εr=336,介电损耗tanδ=0.018,介电常数温度系数τε=-1.5×10-5℃-1。ZB掺杂CCTO基陶瓷的阻抗谱表明:CCTO陶瓷由半导体化晶界和相对绝缘的晶粒构成,因此,其具有巨介电常数。     

化学计量比偏移对钛酸铜钙陶瓷微观结构和电性能的影响

采用固相法制备了偏离化学计量的CCTO陶瓷样品(组成Ca Cu3+xTi4O12,x=–0.12~+0.12),研究发现Cu含量的改变对微观结构和介电性能影响显著。符合化学计量比的Ca Cu3Ti4O12(CCTO)陶瓷微观结构不均匀,部分晶粒发生异常生长,而CCTO晶粒间界存在明显的富Cu相析出。随着Cu含量减少,晶粒平均粒径减小并趋于均匀。电性能测试结果表明,标准化学计量或Cu过量(x=0~0.12)的CCTO陶瓷样品,表观介电系数、压敏电压与样品厚度的关系符合体型或晶界型特征,即表观介电系数与样品厚度无关,压敏电压与样品厚度成正比;减少Cu含量(x=0~–0.12),这种体型或晶界型特征逐渐转变为表面型特征,当x–0.08时,样品的表观介电系数与样品厚度成正比,压敏电压与样品厚度无关,表现出表面效应特征。     

溶胶—凝胶法制备CaCu3Ti4O12-MgTiO3复合陶瓷的介电性能与IV特性

通过溶胶凝胶方法制备得到CaCu3Ti4O12-MgTiO3复合陶瓷粉料,并在1000,1050和1100℃3个温度点烧结成瓷。采用XRD、SEM等对得到的样品成分、结构进行了分析,发现材料为CCTO-MgTiO3/MgTi2O4复相体系。在此基础上,对材料的介电性能、IV非线性特性做了相关测试。复合陶瓷在1100℃下烧结后,其介电常数比纯的CCTO要提高3到4倍。对材料的IV测试发现,复合陶瓷的IV非线性系数可以通过复合体系的线性法则拟合得到,材料的非线性系数约为4.56。     

Bi4Ti3O12掺杂中温烧结(Ba,Sr)TiO3基电容器陶瓷

研究了Bi4Ti3O12掺杂量(≥8%,质量分数)对(Ba,Sr)TiO3(Barium Strontium Titanate,BST)铁电电容器陶瓷介电性能的影响,得到不同Bi4Ti3O12掺杂量与BST陶瓷性能的关系,得到中温烧结(≤1150℃)、高压(≥6.99MV/m)、低损耗(0.008)、符合X7R特性的多层陶瓷电容器瓷料.借助扫描电镜(SEM)研究了Bi4Ti3O12对BST陶瓷微观结构的影响,探讨了Bi4Ti3O12掺杂量对BST陶瓷性能和结构影响机理.结果表明:Bi4Ti3O12是通过与BST形成核-壳结构、形成玻璃相、偏析晶界及抑制晶粒生长、改善介温特性等来影响瓷料性能和结构的.这些结果为Bi4Ti3O12掺杂改性BST电容器陶瓷提供一定的依据.     

烧结温度对CaCu3Ti4O12陶瓷C波段介电性能的影响

采用固相反应法制备了CaCu3Ti4O12(CCTO)陶瓷,研究了烧结温度对CCTO晶相、微观形貌、致密度以及在C波段(3.95～5.85 GHz)的介电性能的影响。结果表明,在1040℃烧结的试样除了含有CCTO,还存在部分没有反应的TiO2。随着烧结温度的升高,TiO2逐渐消失。与1040℃和1060℃烧结的试样相比,在1080℃烧结的试样晶粒尺寸较大且粒径较均匀,而在1100℃烧结的试样有明显的熔化现象。试样的密度随烧结温度的升高而增加,在1080℃时达到最大值。在1040～1080℃烧结的试样,其介电常数随着烧结温度的升高而增加,而在1100℃烧结的试样的介电常数反而有所降低。不同烧结温度下的CCTO陶瓷的介电常数和介电损耗随频率的增大变化不大。在所得的试样中,在1080℃烧结的CCTO陶瓷介电常数最高,介电损耗最低。     

Bi4Ti3O12掺杂中温烧结(Ba,Sr)TiO3基电容器陶瓷

研究了Bi4Ti3O12掺杂量(≥8%,质量分数)对(Ba,Sr)TiO3(Barium Strontium Titanate,BST)铁电电容器陶瓷介电性能的影响,得到不同Bi4Ti3O12掺杂量与BST陶瓷性能的关系,得到中温烧结(≤1150℃)、高压(≥6.99MV/m)、低损耗(0.008)、符合X7R特性的多层陶瓷电容器瓷料.借助扫描电镜(SEM)研究了Bi4Ti3O12对BST陶瓷微观结构的影响,探讨了Bi4Ti3O12掺杂量对BST陶瓷性能和结构影响机理.结果表明Bi4Ti3O12是通过与BST形成核-壳结构、形成玻璃相、偏析晶界及抑制晶粒生长、改善介温特性等来影响瓷料性能和结构的.这些结果为Bi4Ti3O12掺杂改性BST电容器陶瓷提供一定的依据.     

钛钽镁酸钡的合成及其微波介电性

以Ba(Mg1/3Ta2/3)O3为基,通过不同量的Ti取代实验,探讨Ti取代对Ba(Mgx/12Ta2x/12Ti12-x/12)O3瓷(1/3＜x＜4=(简称BMTT)介电性能和结构的影响.结果表明Ti4+与Mg2+,Ta5+离子对构成类质同相代换,形成Ba(Mgx/12Ta2x/12Ti12-3x/12)O3(1/3≤x≤4)系列新固溶体,与Ba(Mg1/3T2/3)O3具有相同的晶体结构.当体系组成蜝a(Mg1/6Ta1/3Ti1/2)O3时,在1480℃下烧结保温3h所制备的材料微波介电性能为εr=89,Q×f=12 700GHz(6GHz下),τf=1.9×10-4/℃.     

高介电常数材料CaCu3Ti4O12的溶胶-凝胶制备技术研究

用溶胶-凝胶(Sol-gel)技术及柠檬酸自燃法,成功制备了新型的纳米CaCu3Ti4O12氧化物超细粉体.将得到的超细粉体压块,并在1000℃高温烧结成微晶陶瓷材料.用X射线粉末衍射(X-ray powdef diffraction,XRD)确定了烧结体的晶相,用扫描电镜(Scanning electron microscopy,SEM)观察了晶粒的形貌特征与大小.同时研究了徽晶陶瓷的介电常数和介电损耗.CaCu3Ti4O12室温介电常数达104,接近目前高介电常数复合含Pb钙钛矿系陶瓷;介电损耗低于0.20.因此,Sol-gel工艺技术是一种制备CaCu3Ti4O12超细粉体与高介电常数微晶陶瓷的有效方法.     

溶胶-凝胶法制备Ni掺杂CaCu3Ti4O12陶瓷的显微组织及电性能（英文）

采用溶胶凝胶法制备掺杂不同含量NiO(CaCu3NixTi4O12+x,x=0, 0.1, 0.2, 0.3)的CCTO陶瓷,通过扫描电镜和 X 射线衍射对其显微组织和相成分进行了分析,并研究了NiO掺杂对CCTO介电和压敏性能的影响。研究结果表明:Ni对CCTO陶瓷的相位成分没有影响,与用传统固相法制得的样品相比,用溶胶-凝胶法制成的样品具有更小的晶粒尺寸。从介电测量结果来看,当 x=0.2 时,样品具有最高的介电常数和最低的介电损耗。当x=0.3时,得到最低的漏电流,最小值为 0.295,同时,具有最高的阀值电压与非线性系数,最大值分别为1326V/mm和3.1。     

Microstructure and electrical properties of Sc2O3-doped CaCu3Ti4O12 ceramics

CaCu3Ti4O12 ceramics doped with different contents of Sc2O3(mol%, x = 0, 0.05, 0.10, 0.15, and 0.20) were prepared by the traditional solid-state reaction method. Scanning electron microscope(SEM) and X-ray diffraction(XRD) were used in the microstructural studies of the specimen, and the electrical properties were investigated. XRD results show that the Sc has no influence on the phase composition. The results from the dielectric measurements show that further increase of Sc doping could decrease the dielectric loss slightly. A high dielectric constant and low dielectric loss can be achieved when the doping concentration is 0.10 mol%.     

Dielectric Properties of Eu-Doped CaCu_3Ti_4O_(12) with Different Compensation Mechanisms

To get a better understanding of the influence of rare-earth element doping,CaCu_3Ti_4O_(12)(CCTO) samples with a partial substitution of Ca with Eu with different compensation mechanisms were designed and prepared by solid-state reaction.All the ceramics were single phase,while the dielectric constants and thermally activated energy values for dielectric relaxation in Eu-doped ceramics were both lower than those of CCTO.Ca_(0.875)Eu_(0.1)Cu_3Ti_4O_(12)(CECT1)exhibited a slight decrease in both the permittivity and electric resistance of grain boundaries compared with CCTO,while Ca_(0.85)Eu_(0.1)Cu_3Ti_4O_(12)(CECT2) underwent a sharp decrease in permittivity associated with an abnormally large resistance.The different dielectric behavior indicates that the dielectric properties of CCTO are sensitive to the valence states of cations and defects.The variation of permittivity is related to the localization of carriers,which,according to the XPS results,should be caused by the presence of oxygen vacancies.The formation of defect complexes between cations and oxygen vacancies leads to the increase in resistance and prevents the hopping between Cu~+ and Cu~(2+),which is an important source of the polarization in grain boundaries.     

Preparation and characterization of Mg-doped CaCu3Ti4O12 thin films

Mg-doped CaCu_3?xMg_xTi₄O₁₂ (x=0, 0.05, 0.1, 0.15, 0.2, at.%) thin films were prepared by a modified sol?gel method. A comparative study on the microstructure and electrical properties of Mg-doped CaCu₃Ti₄O₁₂ (CCTO) thin films was carried out. The grain sizes of the Mg-doped CCTO thin films were smaller in comparison to the undoped CCTO films. Furthermore, compared to undoped CCTO films, Mg-doped CCTO thin films obtained higher dielectric constant as well as excellent frequency stability. Meanwhile, Mg doping could reduce the dielectric loss of CCTO thin films in the frequency range of 10⁴?10⁶ Hz. The results showed that the Mg-doped CCTO thin films had the better electrical characteristics compared with the undoped CCTO films. The nonlinear coefficient of Mg-doped CCTO thin films at x=0.15 and x=0.1 was improved to 7.4 and 6.0, respectively.     

Preparation and Dielectric Properties of CaCu3Ti4O12 Ceramics with Different Additives

Li₂CO₃, MgCO₃, BaCO₃, and Bi₂O₃ dopants were introduced into CaCu₃Ti₄O₁₂ (CCTO) ceramics in order to improve the dielectric properties. The CCTO ceramics were prepared by conventional solid-state reaction method. The phase structure, microstructure, and dielectric behavior were carefully investigated. The pure structure without any impurity phases can be confirmed by the x-ray diffraction patterns. Scanning Electron Microscopy (SEM) analysis illuminated that the grains of Ca_0.90Li_0.20Cu₃Ti₄O₁₂ ceramics were greater than that of pure CCTO. It was important for the properties of the CCTO ceramics to study the additives in complex impedance spectroscopy. It was found that the Ca_0.90Li_0.20Cu₃Ti₄O₁₂ ceramics had the higher permittivity (>45000), the lower dielectric loss (<0.025) than those of CCTO at 1 kHz at room temperature and good temperature stability from ?30 to 75 °C.     

CaCu3Ti4O12 ceramics from basic co-precipitation (BCP) method: Fabrication and properties

High dielectric CaCu₃Ti₄O₁₂ (CCTO) ceramics have been successfully prepared by a novel basic co-precipitation (BCP) method. Compared with the conventional solid-state and/or soft chemistry methods, the BCP method has many advantages such as relatively lower sintering temperature, shorter sintering time and lower costs. The XRD patterns confirm the formation of CCTO crystal phase in the as-prepared samples. Influences of initial ingredients and sintering condition on phase composition, microstructure and dielectric property have been investigated through series of trials. The correlation between the process of the grain growth and dielectric properties of final products has been explored. The final products exhibit the dielectric constants higher than 10,000 and the dielectric losses lower than 0.15 at 1 KHz.     

Dielectric relaxation behaviors of pure and Pr6O11-doped CaCu3Ti4O12 ceramics in high temperature range

Pure and Pr₆O₁₁-doped CaCu₃Ti₄O₁₂ (CCTO) ceramics were prepared by conventional solid-state reaction method. The compositions and structures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of Pr-ion concentration on dielectric properties of CCTO were measured in the ranges of 60 Hz-3 MHz and 290-490 K. The third phase of Ca₂CuO₃ was observed from the XRD of CCTO ceramics. From SEM, the grain size was decreased obviously with high valence Pr-ion (mixing valence of Pr³⁺ and Pr⁴⁺) substituting Ca²⁺. The room temperature dielectric constant of Pr-doped CCTO ceramics, sintered at 1323 K, was an order of magnitude lower than the pure CCTO ceramics due to the grain size decreasing and Schottky potential increasing. The dielectric spectra of Pr-doped CCTO were flatter than that of pure CCTO. The loss tangent of Pr-doped CCTO ceramics was less than 0.20 in 2 × 10²-10⁵ Hz region below 440 K. The complex impedance spectra of pure and Pr-doped CCTOs were fitted by ZView. From low to high frequency, three semicircles were observed corresponding to three different conducting regions: electrode interface, grain boundary and grain. By fitting the resistors R and capacitors C, the activation energies of grain boundary and electrode contact were calculated. All doped CCTOs showed higher activation energies of grain boundary and electrode than those of pure CCTO ceramics, which were concordant with the decreasing of dielectric constant after Pr₆O₁₁ doping.     

Dielectric properties of soft chemical method derived CaCu3Ti4O12 thin films onto Pt/TiO2/Si(1 0 0) substrates

Calcium copper titanate, CaCu₃Ti₄O₁₂ (CCTO), thin film has been deposited by the soft chemical method on Pt/Ti/SiO₂/Si (1 0 0) substrates at 700 °C for 2 h. The peaks were indexed as cubic phase belonging to the Im−3 space group. The film exhibited a duplex microstructure consisting of large grains of 130 nm in length and regions of fine grains (less than 80 nm). The CCTO film capacitor showed a dielectric loss of 0.031 and a dielectric permittivity of 1020 at 1 MHz. The J-V behavior is completely symmetrical, regardless of whether the conduction is limited by interfacial barriers or by bulk-like mechanisms. Based on impedance analyses, the equivalent circuit of CCTO film consisting of a resistor connected in series with two resistor-capacitor (RC) elements.