烧成工艺对CaCu3Ti4O12陶瓷介电性能的影响

采用短时间烧结制备了CaCu3Ti4O12(CCTO)陶瓷,并详细研究了预烧温度、烧结温度等工艺对结构和性能的影响。研究了εr和tanδ随测试频率(20Hz～1MHz)、温度(25～150℃)的变化规律。结果表明:CCTO陶瓷的性能对烧成工艺非常敏感。较低的预烧温度较容易获得高εr(εr为11248)的CCTO陶瓷。     

Effects of Carbon Coating on Microstructure and Dielectric Properties of CaCu3Ti4O12

CaCu₃Ti₄O₁₂ (CCTO) powders coated with carbon were synthesized by using a high-energy ball milling method. The obtained samples were characterized by x-ray diffraction, transmission electron microscopy and scanning electron microscopy. The carbon-coated CCTO particles had a rough surface, which resulted from the growth of the carbon coating on the CCTO particles. It was found that the CCTO phase was observed as the major phase and no reaction occurred between the carbon and CCTO during the sintering process. The grain size of the CCTO ceramics decreased with the increase in carbon content, which indicated that carbon inhibits grain growth of CCTO ceramics. Specially, the dielectric constant decreased with the increase in carbon content. And CCTO1 ceramic (mass ratio of CCTO: carbon = 10:1) showed a lower dielectric constant (3.74 × 10⁴), with the dielectric loss value (0.04) much lower than that of CCTO at 20°C (10 k Hz).     

Thermoelectric Properties and Conduction Mechanism of CaCu3Ti4O12 Ceramics at High Temperatures

The Seebeck coefficient and electrical conductivity of CaCu₃Ti₄O₁₂ (CCTO) ceramics were measured and analyzed in the high temperature range of 300°C to 800°C, and then the electrical conduction mechanism was investigated by using a combination of experimental data fitting and first-principles calculations. The Seebeck coefficient of the CCTO ceramic sintered at 1050°C is negative with largest absolute value of ～650 μV/K at 300°C, and the electrical conductivity is 2–3 orders greater than the value reported previously by other researchers. With increasing sintering temperature, the Seebeck coefficient decreases while the electrical conductivity increases. The temperature dependence of the electrical conductivity follows the rule of adiabatic hopping conduction of small polarons. The calculated density of states of CCTO indicates that the conduction band is mainly contributed by the antibonding states of Cu 3d electrons, therefore small-polaron hopping between CuO₄ square planar clusters was proposed. Possible ways to further improve the thermoelectric properties of CCTO are also discussed.     

Ba2+掺杂对CaCu3Ti4O12陶瓷结构与电性能的影响

采用传统固相法制备了Ca1-xBaxCu3Ti4O12(x=0, 0.005, 0.010, 0.020, 0.030, 0.040, 0.050, 0100,摩尔分数) 陶瓷。用X线衍射仪、扫描电子显微镜、介电温谱测试系统及阻抗测试仪研究了Ba2+掺杂量的变化对Ca1-xBaxCu3Ti4O12陶瓷的相结构、微观形貌及电性能影响。研究结果表明,随着Ba2+掺杂量的增加,陶瓷试样产生了第二相CuO,同时Ba2+掺杂使CaCu3Ti4O12的晶格常数增大。Ca1-xBaxCu3Ti4O12陶瓷的晶粒尺寸随Ba2+掺杂量的增加而减小,气孔率随之降低。掺杂适量的Ba2+可有效降低CaCu3Ti4O12陶瓷的介电损耗,也可降低相对介电常数随温度的变化率。一定量的Ba2+掺杂还能增加CaCu3Ti4O12的晶界电阻。     

Zn取代Cu对CCTO陶瓷高、低频介电性能的影响

采用传统固相法制备了CaCu_((3-x))Zn_xTi_4O_(12)(CCTO,x=0,0.04,0.08,0.12)陶瓷。用X线衍射仪和扫描电子显微镜研究了Zn~(2+)掺杂含量的变化对CaCu_((3-x))Zn_xTi_4O_(12)陶瓷的相结构、微观形貌的影响规律,并研究了CaCu_((3-x))Zn_xTi_4O_(12)陶瓷的低、高频介电性能。结果表明,少量Zn~(2+)的加入影响CaCu_((3-x))Zn_xTi_4O_(12)陶瓷的相结构和微观形貌。在低频范围内,CaCu_((3-x))Zn_xTi_4O_(12)陶瓷均具有巨介电常数(>104),且CaCu_(2.92)Zn_(0.08)Ti_4O_(12)陶瓷的介电常数温度依赖性小,介电损耗最小,这加速了CCTO陶瓷在陶瓷电容器方向应用的潜力。在微波频段(5.85~8.2GHz)范围内,CaCu_((3-x))Zn_xTi_4O_(12)陶瓷均具有介电弛豫现象,CaCu_((3-x))Zn_xTi_4O_(12)陶瓷的介电常数实部随掺杂量的增加而减小,介电常数虚部和损耗对应的频率变化趋势与实部一致。     

中温烧结(Ca0.61,Nd0.26)(Ti0.98Sn0.02)O3微波介质陶瓷制备及介电性能

研究了添加不同CuO-H3BO3含量的(Ca0.61, Nd0.26)(Ti0.98Sn0.02)O3(CNT)陶瓷的烧结行为和介电性CuO-H3BO3 能促使陶瓷在1050 ℃致官烧结而不严重破坏其介电性能.添加5wt% CuO-H3BO3的CNT陶瓷在1050 ℃烧结后具有良好的微波介电性能: εr=92,Q×f =9 250 GHz,τf=+139×10-6/℃.     

不同晶粒尺寸钛锡酸钡陶瓷的烧结及介电性能

利用溶胶包覆和高能球磨的方法,经传统的陶瓷工艺,得到相对密度在95%以上,晶粒尺寸在0.36~23μm之间的Ba(Ti0.9Sn0.1)O3钛锡酸钡陶瓷。发现用溶胶包覆粉体的方法,可以阻止烧结过程中晶粒的异常长大,并且降低陶瓷的烧结温度。对样品介电性能进行了研究,发现随着晶粒尺寸的减小,Ba(Ti0.9Sn0.1)O3陶瓷表现出相对介电常数峰值对应的温度(tm)向低温方向移动,相变弥散程度增加,室温(25℃)相对介电常数先增大后减小的规律。     

Nd2O3掺杂BaZr0.2Ti0.8O3陶瓷的介电性能

在溶胶-凝胶法制备钛酸钡(BaZr0.2Ti0.8O3)超细粉体的过程中,使用液相掺杂的方式在溶胶过程中进行了稀土元素Nd的掺杂。掺杂摩尔分数为0、0.001、0.002、0.003、0.004和0.005。掺杂改性后的BaZr0.2Ti0.8O3粉体,通过X-射线衍射(XRD)测试,结果表明在摩尔分数为0.005以内的稀土Nd掺杂并未改变BaZr0.2Ti0.8O3的钙钛矿结构。粉体烧结的陶瓷介电性能得到较大的改善:介电常数由3 389提高到4 493,而介电损耗在60 Hz时由1.4%降低到0.35%。     

Understanding Phase Segregation Using Rietveld Analysis and the Dielectric,Ferroelectric Properties of Ba (1−x) Ca x TiO 3 Solid Solutions

There isconsiderable disagreement in the reported Ca solubility limit in BaTiO3 (12–50 at.%) synthesised using different techniques and sintering temperatures. Surprisingly, literature reveals a non-monotonic behaviour of Ca solubility in BaTiO3 with regard to sintering temperature. Also, contrasting trends have been reported on the ferroelectric Tc of Ca doped BaTiO3 with respect to BaTiO3. To investigate these issues, bulk samples of Ba1−xCaxTiO3 (0.05 ≤ x ≤ 0.40) were synthesised using the solid state reaction route. X-ray diffraction analysis showed that the samples crystallisd into a pure tetragonal structure up to x ≤ 0.20. Additional impurity peaks corresponding to orthorhombic CaTiO3 were observed for x ≥ 0.25 samples, confirming the Ca solubility in BaTiO3 to be ≈ 20 at.% at 1260°C. Field emission scanning electron microscopy (FESEM) micrographs showed that a x = 0.30 sample exhibited the maximum grain size. The ferroelectric Tc was upshifted as compared to BaTiO3. The maximum Pr was observed for the x = 0.15 sample, and varied inversely with dc conductivity of the samples.     

La2O3对Ba0.92Sr0.08Ti0.9Sn0.1O3介质瓷结构及性能的影响

以碳酸钡、碳酸锶、二氧化锡和二氧化钛等为原料,La2O3为掺杂剂,在不同温度下烧结,制得了Ba0.92Sr0.08Ti0.9Sn0.1O3(BSTS)系介质瓷.XRD结果表明,所有的BSTS试样都形成了单一的钙钛矿结构晶相,通过SEM分析了La2O3对试样的微观形貌的影响,发现La2O3的加入可有效地抑制晶粒的尺寸.测试了在1 kHz频率条件下试样的电容量C、介质损耗因数D和-25～+95 ℃试样的C和D,得到了试样的居里温度TC及相对介电常数εr随温度的变化曲线.结果表明,在室温下,试样的εr随着La2O3加入量的增加,呈一直减小的趋势,介电损耗tan δ随着La2O3加入量的增加,则呈先减小后增加的趋势,TC随着La2O3加入量的增加逐渐向低温区移动,介电常数变化率Δε/ε则随着La2O3加入量的增加而逐渐下降.最终得到烧结温度为1 340 ℃,x(La2O3)=0.6%的Ba0.92Sr0.08Ti0.9Sn0.1O3介质瓷的εr最大值为3 825,tan δ最小值为20×10-4,Δε/ε为25.9%( 25 ～85 ℃).     

Bi4-xLaxTi3O12介电陶瓷的制备及其介电性能的研究

采用固相烧结法制备了不同掺La量、不同烧结工艺的铋层化合物 Bi4-xLaxTi3O12(x=0,0．25,0．5,0．75,1)介电陶瓷。利用宽频LCR数字电桥和XRD、 SEM分析了Bi4-xLaxTi3O12介电陶瓷的晶相和微观结构对其介电性能的影响。研究表明,1050℃烧结温度保温4h的Bi3.5La0．5Ti3O12介电陶瓷,致密性好、晶粒均匀、具有良好的综合介电性能。     

高介电材料CaCu3Ti4O12光电子能谱研究

采用固相反应法制备了CaCu3Ti4O12(CCTO)高介电陶瓷材料,X-射线衍射的结果表明,制备的样品为体心立方结构,晶格常数a=0.737 8 nm。光电子能谱研究结果显示,在CCTO样品中出现了Cu3 和Ti3 ,O1s芯能级谱出现双峰特征。     

Ta、Nb掺杂Bi_(3.15)Nd_(0.85)Ti_3O_(12)陶瓷铁电介电性能研究

采用传统固相烧结工艺制备了掺杂Ta、Nb的Bi3.15Nd0.85Ti3O12材料,构成Bi3.15Nd0.85Ti3-2x TaxNbxO12(x=0,0.02,0.04,0.06)铁电陶瓷。研究了Ta、Nb掺杂对Bi3.15Nd0.85Ti3O12陶瓷晶体结构和铁电性能的影响。结果表明,Ta、Nb掺杂未改变Bi3.15Nd0.85Ti3O12陶瓷的钙钛矿晶体结构,剩余极化值提高,具有较好电滞回线(Pr-Ec)。在电压为45 V、测试频率为0.1kHz下,Bi3.15Nd0.85Ti3-2xTaxNbxO12铁电陶瓷的剩余极化强度(2Pr)及矫顽场强(2Ec)可分别达到25.07μC/cm2和31.1kV/cm,电容-电压(C-V)曲线呈标准的蝴蝶形。     

Preparation and Characterization of Silica-Coated CaCu3Ti4O12

Silica was homogeneously coated on the surface of CaCu₃Ti₄O₁₂ (CCTO) particles via the sol–gel method. The obtained powders were characterized by x-ray diffraction analysis, Fourier-transform infrared spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy, scanning electron microscopy, and zeta potential analysis. The results demonstrate that there were silica layers on the surface of the CCTO particles. Physical and dielectric properties of silica-coated CCTO were also studied. TEM imaging showed that the thickness of the silica layer on the CCTO particles was about 20 nm to 35 nm. The specimen coated with 1.0 wt.% silica showed the maximum relative density of 96.7% with high dielectric constant (12.78 × 10⁴) and low dielectric loss (0.005) at 20°C after sintering at 1000°C for 6 h.     

Dielectric and Piezoelectric Properties of PLZT x/40/60 (x = 5; 12) Ceramics

Russian Microelectronics - The results of studies of the structure, as well as piezoelectric, and dielectric properties, of lead zirconate-titanate ceramics modified with various concentrations of...     

铌酸锌陶瓷的低温烧结与介电性能

采用传统固相反应法合成ZnNb2O6陶瓷粉体。系统研究了添加不同含量V2O5对ZnNb2O6陶瓷的烧结特性及介电性能的影响。结果表明:其烧结温度降低到1 050℃,且当V2O5质量分数大于1.0%时有第二相ZnV2O6生成。添加V2O5后ZnNb2O6陶瓷的谐振频率温度系数向0方向偏移。当V2O5质量分数为1.0%的ZnNb2O6陶瓷在1 050℃烧结3h时,其介电性能为εr=28,tanδ=0.000 6,τf=-42.5×10-6/℃(在1 MHz下)。     

Bi4Ti3O12掺杂对BST陶瓷性能和结构的影响

研究了Bi4Ti3O12(2%～10%,质量分数)掺杂对(Ba0.71Sr0.29)TiO3(BST)基电容器陶瓷介电常数εr、介质损耗tan δ、容温变化率△C/C等性能及其烧结温度的影响.结果表明,当w(Bi4Ti3O12)=10%时,εr为2 558,tan δ为0.005 0,△C/C=-39.2%,△C/C在25～125℃的范围内比在w(Bi4Ti3O12)=2%时降低了18%,陶瓷的烧结温度降为1 180℃.借助SEM和XRD研究了Bi4Ti3O12掺杂量对样品的显微结构和物相组成的影响,表明Bi4Ti3O12作为烧结助剂包裹晶粒并填充晶粒间形成异相,阻止晶粒生长并细化晶粒.     

钛酸钡半导体陶瓷的低温介电特性

在80—320K温度范围内,研究了两种组份BaTiO_3半导体陶瓷的介电特性,发现其介电常数温度曲线不再明显有反映不同铁电相变的两个介电峰,但介电常数实部和虚部的极大值位置分别与mm2—3m和4mm—mm2铁电相变的温度有关。这可能是由于其铁电相变高度弥散、mm2—3m铁电相变温度与Sr~(2-)的取代量基本无关以及4mm相出现PTCR效应的结果。