溶胶凝胶法制备NiO掺杂CaCu3Ti4O12薄膜（英文）

用溶胶凝胶法制备纯CaCu3Ti4O12(CCTO)薄膜以及NiO掺杂CaCu3-x Nix Ti4O12(CCNTO)薄膜(x=0.10、0.20、0.30),研究了掺杂NiO对CCTO介电性能以及微观结构的影响。通过AFM图片可以看出,掺杂NiO的CCTO薄膜的晶粒尺寸比不掺杂NiO的CCTO薄膜的晶粒尺寸小。当x=0.2时,CCNTO薄膜的漏电流最小,最小值为0.546 mA,同时具有最大阈值电压与最大非线性系数,最大值分别为81 V/mm和1.9。当Ni掺杂量达到一定程度时,CCNTO薄膜的介电常数就会增加,总体来说,随着Ni的掺杂量增加,CCNTO薄膜的介电损耗呈上升趋势。     

流延法制备片式CaCu3Ti4O12陶瓷及其性能研究（英文）

片式CaCu3Ti4O12陶瓷由于其巨介电效应,用于制备多层陶瓷片式电容具有重大意义。通过水基流延法并在不同的烧结温度下制备的片式CaCu3Ti4O12陶瓷具有优异的介电性能。其中在1080℃下烧结的样品在保持巨电容率(98605)的同时,降低了介电损耗,其值只有0.028,远低于其他报道的损耗值。同时,测试了CCTO陶瓷薄片的复阻抗图谱,讨论了CCTO陶瓷的特殊的电学性能。实验结果表明,通过流延成型制备的CCTO陶瓷薄片在保持巨电容率的同时具有很低的介电损耗,这为CCTO陶瓷在微电子工业上的应用提供了可能性。     

电极对CaCu3Ti4O12陶瓷介电性能的影响

通过研究在不同气氛(氮气和氧气),CaCu3Ti4O12(CCTO)陶瓷样品在一定温度下进行后处理后,不同功函数电极对其介电性质的影响,进而研究CCTO陶瓷的巨介电常数的起源问题.我们在空气中制备了CaCu3Ti4O12陶瓷,发现样品表面电阻率很大,样品表面呈现绝缘态,此时不同功函数电极以及不同电极制备方法对其介电性质几乎没有影响,说明CCTO的巨介电常数是由孪晶界或半导体晶粒与绝缘晶界所产生的内部阻挡电容(IBLC)所引起.但当样品在高温氮气中后处理后,样品表面电阻率明显下降,以较大功函数的金属作为电极的样品,其介电常数有了明显的提高,而以功函数小的金属作为电极的样品,其介电常数变化不大.从而进一步说明当CCTO样品表面处于半导态,表面电极效应也是CCTO巨介电常数来源之一.     

烧结工艺对B2O3掺杂Ba1-xSrxTiO3梯度陶瓷介电性能的影响

研究了烧结温度及升温速率对氧化硼(B2O3)掺杂钛酸锶钡梯度陶瓷(Ba1-xSrxTiO3,x=0～0.4,步长0.02)的致密化、晶粒尺寸及介电性能的影响.结果表明,随着烧结温度的升高,在氧化硼挥发的同时致密化程度提高,从而居里峰提高且变得尖锐;随着氧化硼含量的增加,晶粒尺寸均匀长大、介电常数和介电损耗都增加;升温速率适中时,掺杂物的挥发、致密化进程及晶粒长大同步完成,梯度陶瓷介电性能才有效提高.此外,钛酸锶钡梯度陶瓷掺杂适量氧化硼明显降低烧结温度,比未掺杂相同成分的陶瓷烧结温度至少降低150℃,且介电损耗明显减小;梯度陶瓷的居里峰温度区间显著展宽,大大降低了该温区的介温系数,可望提高该系列陶瓷元器件精度及稳定性.     

高介电陶瓷材料CaCuaTi4O12的研究现状及展望

CaCu3 Ti4O12(以下简称CCTO)陶瓷是一种非铅基的、具有高介电常数且不随温度明显变化的新型高介电陶瓷材料.介绍了CCTO材料的研究现状,探讨了CCTO材料巨介电性来源,综述了CCTO材料制备工艺的研究以及CCTO材料的掺杂改性研究,并展望了今后的研究路线和思路.     

CaCu3Ti4O12/NiCuZn铁氧体基磁电复合材料研究

将CCTO(CaCu3Ti4O12)与NiCuZn铁氧体进行复合,系统地研究了组分变化对这种新型磁电复合材料的烧结性能、晶相结构、显微结构和磁电性能的影响。随后,为了实现复合材料的低温烧结以及综合考虑复相陶瓷的磁电性能,选取80%(质量分数,下同)NiCuZn铁氧体/20%CCTO组分,以BBSZ(Bi2O3-H3BO3-SiO2-ZnO)玻璃作为助熔剂,研究了CCTO/NiCuZn铁氧体基复合材料的烧结行为和磁电性能。结果表明,掺杂BBSZ后,900℃下烧结的所有样品的密度均达到了复相陶瓷理论密度的95%,且复相陶瓷的介电常数和磁导率在1～30 MHz范围内均不依赖于频率的变化。在10 MHz的频率下,当BBSZ的含量从0增加到3%时,复相陶瓷磁导率μ从13.2增加到47.9,磁损耗tanδμ从0.022下降到0.017,同时,样品的谐振频率从109Hz左右移动到3.2×108Hz。相应地,复相陶瓷的介电常数ε从9.2增加到16,介电损耗tanδε从0.069下降到0.012。这一优异的整体性能使其有望实际应用。     

V2O5对 BaTiO3-Y2O3-MgO陶瓷性能的影响

研究了V2O5掺杂BaTiO3-Y2O3-MgO系陶瓷的显微结构和介电性能．SEM显示V2O5会促进该体系晶粒生长，降低陶瓷致密度．XRD显示V掺杂样品均为单一赝立方相，其固溶度〉1．0m01％．研究表明，V离子能有效抑制掺杂离子Y、Mg向BaTiO3晶粒内扩散，改变掺杂离子在晶粒中分布，从而形成薄壳层的壳芯晶粒，因此V能提高居里峰的强度并改善电容温度稳定性．多价V离子在还原气氛中以＋3、＋4为主，能增强瓷料的抗还原性，提高绝缘电阻率（10^13Ω·cm）、降低介电损耗（0．63％）．该体系掺杂0．1mol％V时，介电常数达到2600，满足X8R标准．     

La2O3掺杂对BST/MgO复合陶瓷显微结构和性能的影响

采用固相反应法制备了未掺杂和La2O3掺杂(0.5%、1%、2%(摩尔分数))的Ba0.55Sr0.45TiO3/MgO复合陶瓷材料,并研究了它们的显微结构和各种介电性能.研究结果表明,La2O3除一部分会进入BST晶格獭代Ba或Sr的位置外,还会有一部分与MgO等形成无定形态物质滞留在晶界,起到抑制BST晶粒生长的作用.BST/MgO复合陶瓷的居里温度随La2O3掺杂量的增大而降低,居里温度的降低导致了介电常数的减小.适量的La2O3掺杂提高了复合陶瓷的调谐性,而且La2O3掺杂明显降低了复合陶瓷的微波介电损耗.0.5%(摩尔分数)La2O3掺杂的BST/MgO复合陶瓷具有最佳的综合介电性能,其在10kHz下的调谐性为6.9%(2kV/mm),3.99GHz时的介电常数和介电损耗分别为87.5和3.35×10-3,基本可以满足铁电移相器的使用要求.     

非化学计量比巨介电CaCu_3Ti_4O_(12)陶瓷研究

采用固相反应法制备了不同化学计量比的CaCu3Ti4O12(简称CCTO)陶瓷。当Ca、Cu、Ti的原子摩尔比为1.08∶3.00∶4.44时,获得了相对介电常数在1kHz下高达4×105(1kHz)的巨介电CCTO陶瓷,其介电常数比标准化学计量比CCTO陶瓷高约一个数量级。结合XRD、SEM、EDX等分析表征结果,对巨介电常数的物理机理进行了探讨。     

Sm2O3掺杂BaTiO3陶瓷的结构与电性能研究

采用溶胶-凝胶法制备了掺杂不同浓度Sm2O3(分别为0.001,0.002,0.003,0.005,0.007mol)的BaTiO3陶瓷,并对其结构与电性能进行了研究.结果表明:Sm2O3掺杂BaTiO3陶瓷的晶型在室温下为四方相,而且随着Sm2O3掺杂浓度的增加,BaTiO3陶瓷的晶粒尺寸变小,说明Sm2O3掺杂对BaTiO3陶瓷晶粒的生长有一定的抑制作用;Sm2O3掺杂BaTiO3陶瓷的电阻率比纯BaTiO3陶瓷明显下降,当添加量为0.001mol时,电阻率最小,.从4.3×109Ω·m下降为6.536×103Ω·m;Sm2O3掺杂BaTiO3陶瓷的晶粒电阻随着温度的变化,呈现NTC效应,而晶界电阻随着温度的变化,呈现PTC效应,且晶界电阻远远大于晶粒电阻,说明该材料的PTC效应是由晶界效应引起的.     

Abnormal dielectric behaviors in Mn-doped CaCu3Ti4O12 ceramics and their response mechanism

Mn-doped CaCu₃Ti₄O₁₂ (CCTO) polycrystalline ceramics have been prepared by the conventional solid state sintering. Our results indicate that 10% Mn doping can decrease the dielectric permittivity in CaCu₃Ti₄O₁₂ by about 2 orders of magnitude (from 10⁴ to 10²). The grain and grain boundary activation energies show an obvious increase from 0.054 eV to 0.256 eV, and decrease from 0.724 eV to 0.258 eV with increasing the Mn doping concentration, respectively, which may be caused by the variation of Cu and Ti valence states in the CCTO samples evidenced by the X-ray absorption spectra. The similar grain and grain boundary activation energies result in invalidation of the internal boundary layer capacitance effect for the 10% Mn-doped CCTO sample, and thus result in the dramatic decrease of dielectric permittivity.     

Effect of copper-oxide segregation on the dielectric properties of CaCu3Ti4O12 thin films fabricated by pulsed-laser deposition

We investigated the effects of post-deposition cooling conditions on the surface morphologies and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) thin films grown by pulsed-laser deposition on Pt/TiO₂/SiO₂/Si substrates. CCTO thin films cooled under the typical cooling parameters, i.e., slow cooling (3 °C/min) at high oxygen pressure (66 kPa) showed a severe segregation of nanoparticles near the grain boundaries, which was identified to be copper oxide from electron probe micro analyzer mapping. On the other hand, we could not observe any segregation on the film surface when the samples were cooled fast (∼ 20 °C/min) at relatively low oxygen pressure (100 Pa). The dielectric constant, ε_r, of CCTO thin films deposited at 750 °C with severe surface segregation (ε_r ∼ 750 at 10 kHz) was found to be much lower than that (ε_r ∼ 2000 at 10 kHz) of CCTO thin films with smooth surface. As the copper-oxide segregation becomes more serious, which preferentially occurs at relatively high ambient oxygen pressure and temperature, the degradation in the dielectric properties of CCTO films becomes larger. The variation of dielectric constant of CCTO films with no copper-oxide segregation could be related to the presence of an impurity phase at grain boundaries.     

The influence of the segregation of Cu-rich phase on the microstructural and impedance characteristics of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

The influence of sintering conditions on the microstructural features and impedance characteristics of the giant dielectric constant material CaCu₃Ti₄O₁₂ (CCTO) was investigated. The microstructure and impedance characteristics were found to be strongly dependent on the sintering conditions. Sintering of the CCTO ceramics at elevated temperatures (>1100 °C) for prolonged durations resulted in the segregation of Cu-rich phase, mostly confined to the surface, which was in concomitance with the appearance of the additional semicircle at the low frequency end in Impedance (Z*) plots. The absence of this additional semicircle in the Cu-deficient CCTO ceramics and the appearance of the same in Cu-rich CCTO ceramics that were deliberately fabricated corroborated the above observations. Also, La_2/3Cu₃Ti₄O₁₂ (LCTO), a low dielectric constant member of CCTO family, which consisted of small grains without the segregation of Cu-rich phase at the grain boundary, did not reveal the presence of additional semicircle in the Z*plots.     

Sol-gel derived CaCu3Ti4O12 ceramics: Synthesis, characterization and electrical properties

The giant dielectric constant material CaCu₃Ti₄O₁₂ (CCTO) has been synthesized by sol-gel method, for the first time, using nitrate and alkoxide precursor. The electrical properties of CCTO ceramics, showing an enormously large dielectric constant ? ∼ 60,000 (100 Hz at RT), were investigated in the temperature range from 298 to 358 K at 0, 5, 10, 20, and 40 V dc. The phases, microstructures, and impedance properties of final samples were characterized by X-ray diffraction, scanning electron microscopy, and precision impedance analyzer. The dielectric permittivity of CCTO synthesized by sol-gel method is at least three times of magnitude larger than that synthesized by other low-temperature method and solid-state reaction method. Furthermore, the results support the internal barrier layer capacitor (IBLC) model of Schottky barriers at grain boundaries between semiconducting grains.     

CaCu3Ti4O12 ceramics from different methods: microstructure and dielectric

CaCu₃Ti₄O₁₂ (CCTO) ceramics were synthesized by methods of sol–gel, traditional solid-state reaction, and thermal decomposition of organic solution. The results exhibit that the microstructures and electric characteristics are affected by the methods of synthesis. The X-ray diffraction patterns show that all samples have a perovskite-like CCTO phase. Moreover, CCTO ceramic from traditional solid-state reaction have the phases of TiO₂ and CuO. The scanning electron microscopy images show that CCTO ceramics from different methods have different grain sizes, grain boundaries, and densities. Dielectric properties of the CCTO ceramics were characterized in a broad frequency range (10–10⁷ Hz) at room temperature. The CCTO ceramics from thermal decomposition of organic solution have the dielectric constant of more than 5 × 10⁴ at 10 Hz. The nonlinear relationship between the current density and the electric field strength can be observed in all the three samples.     

尖晶石型CuAl2O4掺杂对CaCu3Ti4O12陶瓷介电性能的影响

研究了尖晶石型CuAl₂O₄掺杂对CaCu₃Ti₄O₁₂陶瓷显微结构、介电性能以及松弛特征和缺陷结构的影响。在频率为10^-1~10⁷ Hz、温度为153~453 K的条件下测量了样品的介电性能。研究表明, 适量添加CuAl₂O₄, 使样品晶粒尺寸减小并趋于均匀, 击穿场强从CaCu₃Ti₄O₁₂陶瓷样品的3.0 kV/cm提高到13.0 kV/cm, 低频介电损耗减小。介电松弛中的高频松弛过程起源于晶粒本征缺陷的电子松弛过程, 其活化能~0.10 eV基本不变; 随着CuAl₂O₄含量增加, 与界面相关的松弛活化能从0.50 eV减小到0.22 eV, 可能与CuAl₂O₄在样品中引入杂质及更复杂的界面有关; 电导活化能从0.66 eV增至0.86 eV, 归因于CuAl₂O₄第二相抑制了晶界处的载流子跳跃, 提高了Schottky势垒高度。CuAl₂O₄掺杂量大于100mol%, 过量CuAl₂O₄会导致样品晶界势垒崩塌, 样品失去非欧姆特性和巨介电性能。     

Dielectric and non-Ohmic properties of CaCu3Ti4O12 ceramics modified with NiO, SnO2, SiO2, and Al2O3 additives

In order to conciliate dielectric and non-Ohmic properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics, NiO, SnO₂, SiO₂, and Al₂O₃ were added as sintering aids to promote the grain growth of CCTO ceramics. Microstructure, dielectric properties, and non-Ohmic behavior of the CCTO ceramics were investigated. Among them, NiO-modified CCTO exhibits good dielectric and non-Ohmic properties (ε = 69833, tanδ = 0.073, α = 3.66 and E _B = 296.7 V/cm), due to NiO is also one of giant dielectric materials. Therefore, it is suitable for applying semiconductor circuits. The relationship between electrical current density (J) and electrical field (E) demonstrated that Schottky barrier should exist at grain boundaries. Non-linear coefficient α was directly proportional to the height of barrier. Depressing barrier width would improve significantly dielectric permittivity but decrease breakdown voltage.     

Low-temperature synthesis of CaCu3Ti4O12 powders, ceramics and thin films via an organic solution

The giant-dielectric-constant material CaCu₃Ti₄O₁₂ (CCTO) was synthesized via an organic solution containing stoichiometric amounts of the metal cations, which is done at lower temperature and shorter reaction time than the conventional solid-state reaction. A stable solution was prepared by dissolving calcium nitrate, copper nitrate, and tetrabutyl titanate in grain alcohol. CCTO powders, ceramics and thin films were synthesized via the solution. The phases, microstructures, and dielectric properties of samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and dielectric spectroscopy. XRD results identify both samples as single phase CCTO. The CCTO ceramics has a low-frequency permittivity of 3.5 × 10⁴. The CCTO thin films has a low-frequency permittivity of 3.1 × 10⁴. Both the CCTO ceramics and CCTO thin films exhibit two dielectric relaxations at room temperature. The low leakage current density of CCTO thin films shows that it is suitable for memory device applications.     

细晶粒BaTiO3陶瓷的微结构及介电性能测试

采用放电等离子烧结技术,在９００℃下得到细晶粒尺寸的、均匀的、纯ＢａＴｉＯ_３陶瓷。对样品的高分辨电镜分析表明,晶粒中只有１８０°电畴,没有９０°电畴,晶界宽度相当于两倍的晶格常数．同时观察到有部分孪晶出现．对细晶粒陶瓷介电性能的测量表明,介电常数对晶粒尺寸有明显的依赖关系,认为李晶的存在是导致小晶粒陶瓷介电常数没有迅速降低的原因之一．对这一效应,用通常的串、并联模型不能很好地拟合。