溶胶-凝胶法合成Ba0.6Sr0.4TiO3/MgO及介电性能研究

采用溶胶-凝胶法合成了Ba_(0.6)Sr_(0.4)TiO_3/MgO复合粉体,研究了烧结温度和合成工艺对陶瓷样品介电性能的影响。研究结果表明,经650℃热处理即可得到颗粒细小均匀的超细Ba_(0.6)Sr_(0.4)TiO_3/MgO粉体,平均粒径在200 nm左右。烧结温度对陶瓷样品的介电生能有明显的影响,1300℃烧结的陶瓷样品具有优良的性能。与二步合成工艺相比,一步合成工艺制备的陶瓷样品具有更好的介(?)性能。     

BaxSr1-xTiO3的EDTA-柠檬酸法合成、制备及介电性能

以EDTA和柠檬酸为复合络合剂,采用溶胶-凝胶法合成了BaxSr1-xTiO3(x=0.5,0.6,0.7)粉体。采用TG-DSC、XRD、SEM对粉体的合成过程、晶体结构及颗粒形态进行了表征。采用固相法制备了BaxSr1-xTiO3陶瓷,并对陶瓷的烧结性能和介电性能进行了研究。研究结果表明,经550℃热处理即可得到单一钙钛矿结构的超细粉体,粉体颗粒分布均匀,平均粒径在100nm左右。在1250￣1300℃烧结的陶瓷样品平均粒径为3￣5μm,相对密度达到95%以上。陶瓷样品在室温下处于顺电相,在同一频率下其相对介电常数随Sr含量的增加而变大。在室温和1kHz的条件下,x=0.5、x=0.6和x=0.7的陶瓷样品的相对介电常数分别为1540、3220和4750,介电损耗分别为0.2%、0.2%和2.1%。     

新型纳米材料Ca0.8Sr0.2TiO3:Pr的合成及表征

文章采用溶胶-凝胶法合成Ca0.8Sr0.2TiO3：Pr纳米粉体，用X射线衍射，TG—DTA测试技术，紫外可见光吸收光谱进行结构表征，分析了不同温度下Ca0.8Sr0.2TiO3：Pr的粒径大小以及结构变化。     

退火温度对BaTiO3薄膜的结构和介电性能的影响

采用溶胶-凝胶法制备Si(100)基片上的BaTiO3陶瓷薄膜,并用红外光谱(IR)、x射线衍射(XRD)、扫描探针(SPM)等技术分析了钛酸钡凝胶的热解过程,以及不同退火温度下薄膜的晶粒、晶相、表面形貌、介电性能等指标.实验结果表明:高温有利于钛酸钡由立方相向四方相的转化;温度升高到1023 K时,钛酸钡薄膜的表面形貌平整、均匀并具有良好的介电性能.     

退火温度对BaTiO_3薄膜的结构和介电性能的影响

采用溶胶-凝胶法制备Si（100）基片上的BaTi03陶瓷薄膜,并用红外光谱（IR）、x射线衍射（XRD）、扫描探针（SPM）等技术分析了钛酸钡凝胶的热解过程,以及不同退火温度下薄膜的晶粒、晶相、表面形貌、介电性能等指标。实验结果表明：高温有利于钛酸钡由立方相向四方相的转化;温度升高到1023K时,钛酸钡薄膜的表面形貌平整、均匀并具有良好的介电性能。     

BaTiO3薄膜的Sol-gel法制备及其介电特性研究

以钛酸四丁酯和乙酸钡为主要原料,以乙二醇独甲醚为溶剂,采用溶胶凝胶法成功地配制出了BaTiO3溶胶,溶胶清晰稳定,保存时间长.并用XRD分析了沉积在Si(100)低阻硅片上的薄膜的结构,发现薄膜在600℃时结晶状态已良好.文中同时对薄膜的介电性质进行研究,并讨论了退火温度对薄膜介电性质的影响.     

溶胶—凝胶法制备Fe2O3—Mn2O3—SiO2膜

用溶胶－凝胶法在浮法玻璃上制备了Ｆｅ２Ｏ３－Ｍｎ２Ｏ３－ＳｉＯ２膜。对膜层的形成特性进行了观察。得出了制备良好膜层的工艺参数。对薄膜的微观结构和光谱特性进行了测定。讨论了薄膜中铁与锰的价态和配位状态。     

La0.6Sr0.4Fe0.8Co0.2O3的甘氨酸-硝酸盐法合成与表征

采用甘氨酸-硝酸盐法(GNP)制备La0.6Sr0.4Fe0.8Co0.2O3初级粉料, 研究甘氨酸用量对初级产物和热处理产物的晶体结构和显微形貌的影响, 并用直流四探针法测量烧结体的电导率.在286.8～365.7 ℃范围内, 初级粉料中残余有机物和残碳氧化分解.钙钛矿结构La0.6Sr0.4Fe0.8Co0.2O3在720.9 ℃左右形成.经750 ℃(保温1 h)热处理即可制得单相钙钛矿结构La0.6Sr0.4Fe0.8Co0.2O3.甘氨酸-硝酸盐法所制粉体颗粒细小, 有轻微烧结现象, 这是由燃烧温度高导致的, 经短时间研磨后团聚状况可得到改善.与固相合成法相比, GNP法所制样品的电导率较高.     

不同制备方法下的La0.8Ca0.2MnO3巨磁阻薄膜的形貌特征研究

采用了固相粉末烧结法、脉冲激光沉积法(Pulsed Laser Deposition)和溶胶—凝胶法(sol—gel)3种方法,制备出了La0.8Ca0.2MnO3(LCMO)巨磁阻粉末样品和在硅基底上诱导生长的薄膜样品。用原子力显微镜(AFM)、光学显微镜以及X射线衍射(XRD)对所得样品进行了结构表征。系统地研究了热处理条件对LCMO结晶形貌的影响。结果发现硅基底上的LCMO薄膜因受到诱导从而呈现出定向生长的现象,表现为类似“花”状的形态;对于固相法制备的样品,则呈现出无定型的多晶形态;对于脉冲激光沉积法制备的样品呈现出均匀致密的多晶薄膜。     

Ba0.5 Sr0.5 TiO3/PMMA复合材料介电性能研究

采用溶胶凝胶法（sol-gel）制备了Ba0．5Sr0．5TiO3／PMMA复合材料粉体。应用红外光谱（IR）、偏光显微镜（PLM）、扫描电镜（SEM）等分析手段，对样品进行了表征与分析，研究了乙烯基三乙氧基硅烷偶联剂在BST55／PMMA复合材料制备过程中起的桥联作用，并讨论了MMA和BST55物质的量比与其介电性能的关系。结果表明，在凝胶化过程中，适量的偶联剂不仅起着交联剂的作用，而且能改善复合材料的粒子聚集态；而复合材料的介电常数远远低于BST55陶瓷，且随着PMMA含量的增加而有所降低。     

Effect of Gd doping on electrical transport properties of La0.8Sr0.2MnO3 polycrystalline ceramics

Gd doped La_0.8Sr_0.2MnO₃ (La_0.8-xGd_xSr_0.2MnO₃, LGSMO) ceramics were prepared by a sol-gel method. X-ray diffraction (XRD) patterns showed that all samples exhibited distorted perovskite structures, R_3c. When the Gd³⁺ content x > 0.03, the crystal structure changed to orthorhombic, Pnma. Scanning electron microscopy (SEM) images showed that the ceramics characterize high density and grain boundary connectivity, and higher Gd³⁺ doping decreased the grain size from 26.72 μm to 7.42 μm. The temperature dependence of resistivity showed a transition from a low-temperature metal to a high-temperature insulator. The resistivity increased with Gd doping content, and the metal-insulator transition temperature, T_P, increased first and then decreased, while the temperature coefficient of resistance (TCR) of the samples first decreased and then increased with Gd³⁺, and the magnetoresistance (MR) increased first and then decreased. The peak TCR at x = 0.06 was 5.18%·K^?1, and MR at 0.04 was 34.57%. The electrical transport properties of the ceramics were explained based on the double exchange (DE) interaction mechanism. The obtained material may have application prospects in magnetic devices and infrared detectors.     

Effect of calcination temperature on optical,magnetic and dielectric properties of Sol-Gel synthesized Ni0.2Mg0.8-xZnxFe2O4 (x = 0.0–0.8)

The Ni_0.2Mg_0.8-xZn_xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6 & 0.8) nanomaterials were prepared via sol-gel technique. These samples were calcined at three different temperatures (T) such as 400, 450 and 500 °C/5 h. Furthermore, the X-ray diffraction (XRD) patterns of all the calcined samples revealed the single phase cubic spinel structure. The lattice constants (a = b = c) were noticed to be increasing with increase of ‘x’. The grain shape, size and distribution of x = 0.0–0.8 contents were analyzed using field emission electron microscope (FESEM). The x = 0.2 content provided higher optical band gap energy (E_g) value than the remaining contents. Furthermore, the magnetization versus magnetic field (M − H) curves indicated the superparamagnetic nature of x = 0.0–0.8 contents. The high saturation magnetization (M_s) was noticed for x = 0.4 and 0.6 contents. In addition, the distribution of cations like Ni⁺², Mg⁺², Zn⁺², Fe⁺³ and Fe⁺² was performed between the tetrahedral (A) and octahedral (B) sites. The frequency dependence of dielectric constant (ε′), dielectric loss (ε") and ac-electrical conductivity (σ_ac) was investigated as a function of composition. Moreover, the temperature variation of ε′ showed the decreasing trend of dielectric transition temperature (T_e) with increase of ‘x’. The high ε′ of 163.1 (at 1 MHz) was noticed at x = 0.2 content calcined at 500 °C. Using the power law fit applied to the log σ_ac-log ω plots, the dc-electrical conductivity (σ_dc) and exponent (n) parameters were calculated.     

Structural,capacitive and resistive characteristics of (Pb0.6Bi0.2Sm0.2)(Fe0.4Ti0.6)O3

Samarium substituted BiFeO₃–PbTiO₃ ceramic compound of (Pb_0.6 Sm_0.2 Bi_0.2)(Fe_0.4Ti_0.6)O₃ has been fabricated by mixed oxide solid state reaction method. The crystallographic structure from XRD study, distribution of grains from SEM micrograph, dielectric behavior, conductivity spectrum, impedance along with electric modulus spectroscopy have been illustrated. The experimental results corroborate the impact of samarium substitution in BiFeO₃–PbTiO₃ entailing reduced grain size, higher dielectric response with reasonably dielectric loss and enrichment in capacitive behavior with negative temperature coefficient of resistance. The temperature dependent conductivity spectra exhibit Arrhenius behavior, whereas the frequency dependent conductivity spectra follow the Jonscher universal power law. The basic correlated barrier hopping (CBH) model governs the charge transport mechanism in the fabricated compound. The exploration reveals the enriched dielectric and electrical behavior that endorse the samarium substituted material as a potential ceramic entity for designing electronic devices such as capacitors and ferroelectric accessories.     

Enhanced dielectric and energy-storage properties in BiFeO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 thin films

Lead free Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ thin films doped with BiFeO₃ (abbreviated as BNKT-xBFO) (x = 0, 0.02, 0.04, 0.08, 0.10) were deposited on Pt(111)/Ti/SiO₂/Si substrates by sol-gel/spin coating technique and the effects of BiFeO₃ content on the crystal structure and electrical properties were investigated in detail. The results showed that all the BNKT-xBFO thin films exhibited a single perovskite phase structure and high-dense surface. Reduced leakage current density, enhanced dielectric and ferroelectric properties were achieved at the optimal composition of BNKT-0.10BFO thin films, with a leakage current density, dielectric constant, dielectric loss and maximum polarization of < 2 × 10⁻⁴ A/cm³, ~ 978^, ~ 0.028 and ~ 74.13 μC/cm² at room temperature, respectively. Moreover, the BNKT-0.10BFO thin films possessed superior energy storage properties due to their slim P-E loops and large maximum polarization, with an energy storage density of 22.12 J/cm³ and an energy conversion efficiency of 60.85% under a relatively low electric field of 1200 kV/cm. Furthermore, the first half period of the BNKT-0.10BFO thin film capacitor was about 0.15 μs, during which most charges and energy were released. The large recoverable energy density and the fast discharge process indicated the potential application of the BNKT-0.10BFO thin films in electrostatic capacitors and embedded devices.     

Microwave sintered Bi0.90La0.10Fe0.95Mn0.05O3 nanocrystalline ceramics: Impedance and modulus spectroscopy

Multiferroic Bi_0.90La_0.10Fe_0.95Mn_0.05O₃ (BLFMO) nanoceramics were synthesized by PVA sol-gel method, followed by microwave sintering. The structural, microstructural and electrical properties of BLFMO were investigated. The crystal symmetry and unit cell dimensions were determined from the experimental data using Rietveld analysis. BLFMO revealed only one electroactive region as verified from impedance and modulus spectroscopy. Overlapping large polaron tunneling transport mechanism was observed from AC conductivity analysis. Conduction below 250 °C (−30 °C≤T≤250 °C) was attributed to translational hopping while above 250 °C (250 °C≤T≤350 °C) corresponds to electron hopping between charge defects. The relative permittivity varies from 66 to 203 at 1 kHz over the measured temperature range (−150 °C≤T≤350 °C). The electrical conductivity of the microwave sintered BLFMO has been discussed based on defect reaction with Mn doping. The measured DC conductivity in the range of 10⁻¹³ S/cm at −130 °C to 10⁻⁴ S/cm at 350 °C revealed the insulating behavior of the sample. At room temperature, the DC resistivity of the sample was over ~50 MΩ cm. The stretching constant (β) obtained from KWW (Kohlrausch-Williams-Watts) equation indicates that the sample inclined towards ideal Debye behavior as the temperature increases.     

Moisture Effect on La0.8Sr0.2MnO3 and La0.6Sr0.4Co0.2Fe0.8O3 Cathode Behaviors in Solid Oxide Fuel Cells

Moisture effect on cathode behaviors is a major issue for solid oxide fuel cells servicing under severe high temperature environments. This work studies the effect of dry air and moist air on La_0.8Sr_0.2MnO₃ (LSM821) and La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF6428) cathodes at 800 °C by investigating the interfacial reaction and degradation through an AISI 441 interconnect/LSM821 (LSCF6428) electrode/yttria‐stabilized zirconia (YSZ) electrolyte tri‐layer structure. Under the same processing condition, the grain size of the LSCF6428 cathode is smaller than that of the LSM821 cathode. Ohmic resistance and polarization resistance of the cathodes are analyzed by deconvoluting the electrochemical impedance spectroscopy (EIS) results. The LSCF6428 cathode has much smaller resistance than the LSM821 cathode. Moisture produces a larger effect on the ohmic resistance and polarization resistance of the LSM821 cathode than on those of the LSCF6428 cathode. More chromium diffuses from the interconnect to the cathode for both LSM821 and LSCF6428 electrodes thermally treated in moist air. Based on the structure, elemental distribution, and EIS analysis, the interaction mechanisms between the electrodes and the AISI 441 alloy interconnect are proposed.     

Structure,electrical and dielectric properties of Ca substituted BaTiO3 ceramics

BaTi_1-xCa_xO_3-x [BTC100x] ceramics were synthesized via solid-state reaction method. Effect of Ca substitution on the structure, electrical and dielectric properties of BTC100x ceramics was systematically investigated. Calcined BTC100x powders were in tetragonal phase when x?≤?0.01, whereas transformed to cubic at x?>?0.01. Additionally, the diffraction peak (200) shifted to lower angles with increasing x, indicating increased unit cell volume. Meanwhile, Ba_0.97Ca_0.03TiO₃ [BC3T] ceramic was prepared and studied, to compare with BaTi_0.97Ca_0.03O_2.97 (BTC3). It was found that pure BaTiO₃ [BT] and BC3T ceramics had the similar structural and dielectric properties, whereas BTC3 ceramic showed much difference,XRD patterns, Raman spectrum, impedance spectra and dielectric-temperature spectra provided strong evidence of Ca²⁺ substitution at Ti site in BT lattice. Finally, BTC100x ceramics were produced and dielectric properties were investigated. With increasing x, the Curie temperature decreased from 128?°C (BT) to 42?°C (BTC5).     

Tuning the microwave dielectric properties of Zn2SnO4 ceramics by adding Ca0.8Sr0.2TiO3

The influence of sintering temperature on the microwave dielectric properties and microstructure of the (1−y)Zn₂SnO₄–yCa_0.8Sr_0.2TiO₃ ceramic system were investigated with a view to their application in microwave devices. A (1−y)Zn₂SnO₄–yCa_0.8Sr_0.2TiO₃ ceramic system was prepared by the conventional solid-state method. The X-ray diffraction patterns of the 0.85Zn₂SnO₄–0.15Ca_0.8Sr_0.2TiO₃ ceramic system did not significantly vary with sintering temperature. A dielectric constant of 9.6, a quality factor (Q×f) of 15,900 GHz, and a temperature coefficient of resonant frequency of −4 ppm/°C were obtained when the 0.85Zn₂SnO₄–0.15Ca_0.8Sr_0.2TiO₃ ceramic system was sintered at 1175 °C for 4 h.     

Enhanced dielectric characteristics of Ba0.94Bi0.04(Fe0.5Nb0.5)O3 coated with SiO2 and SiO2/Al2O3 over a broad frequency and temperature range

Pure phase of Ba_0.94Bi_0.04(Fe_0.5Nb_0.5)O₃ (BBFN) nano-particles were obtained by chemical co-precipitation method. The core-shell structure of BBFN@SiO₂ and BBFN@SiO₂/Al₂O₃ particles and the target ceramics were successfully prepared by aqueous chemical coating approach. The microstructures and dielectric properties of BBFN@SiO₂ and BBFN@SiO₂/Al₂O₃ were studied. Both the BBFN@SiO₂ and BBFN@SiO₂/Al₂O₃ samples show significantly decreased dielectric loss and good frequency and temperature stability on relative permittivity. Compared to the rapid decline of relative permittivity of BBFN@SiO₂, the synergistic effect of SiO₂ and Al₂O₃ in BBFN@SiO₂/Al₂O₃ ceramics made the relative permittivity of which remains a relatively high level with very low dielectric loss, making it more suitable in colossal permittivity applications. Based on the impedance analysis, the grain boundary effect and IBLC models play the important role for the improvement of dielectric properties of BBFN@SiO₂/Al₂O₃ samples.     

Microstructure and microwave-frequency electromagnetic properties of Ni0.4Zn0.6Fe2O4/Ba0.6Sr0.4TiO3 composites

(x)Ni_0.4Zn_0.6Fe₂O₄+(1−x)Ba_0.6Sr_0.4TiO₃ composite ceramics with x=0.6, 0.7, 0.8, 0.9 and 1 were synthesized by solid state reaction method. The high dense composites have only two phases, i.e., Ni_0.4Zn_0.6Fe₂O₄ and Ba_0.6Sr_0.4TiO₃. The permittivity ε′ of the composites decreases slightly with the frequency increasing from 3 MHz to 1 GHz. The permittivity ε′′ of the composites also shows a little increase with frequency in the 3 MHz–1 GHz range. The permeability displays a relaxation resonance within the 3 MHz–1 GHz frequency range. The permeability μ′ increases while the cut-off frequency decreases with the Ni_0.4Zn_0.6Fe₂O₄ concentration, obeying the Snoek's law μ_if_r=constant. The permittivity ε′ of the composites decreases with Ni_0.4Zn_0.6Fe₂O₄ concentration. The composites have a relatively higher ε′ than the pure Ni_0.4Zn_0.6Fe₂O₄ at 1–10 GHz. In the frequency range of 1–10 GHz, the magnetic permeability μ′ reaches its maximum and μ′′ shows a minimum for the composite with x=0.6 in all ceramics. The permeability μ′ of the composites decreases with dc magnetic field at 1–10 GHz. The permeability shows a domain wall resonance, and the resonance frequency shifts to high frequency with the dc magnetic field. The permittivity was also influenced by the dc magnetic field due to a magnetodielectric effect.