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。     

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。     

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%。     

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.     

溶胶凝胶自燃烧法合成Mn0.6Cu0.2Zn0.2O(Fe2O3)0.98纳米晶铁氧体及其磁性能研究

利用溶胶凝胶自燃烧法 ,在室温下直接合成了 30nm左右的Mn0 .6 Cu0 .2 Zn0 .2 O(Fe2 O3) 0 .98纳米晶铁氧体。借助于DTA -TG ,IR ,XRD和VSM技术 ,对干凝胶的热分解过程 ,自燃烧本质及合成纳米晶的磁性能进行了研究。研究表明 ,由金属的硝酸盐和柠檬酸形成的干凝胶具有自燃烧的特性。自燃烧的实质是在热诱导下的氧化还原反应。XRD结果表明 ,通过自燃烧反应可以直接获得纯的锰铜锌铁氧体相而无Fe2 O3相的存在。当对自燃烧粉进行预烧时 ,随着预烧温度的提高 ,有Fe2 O3相的出现。随着预烧温度的升高 ,Mn0 .6 Cu0 .2 Zn0 .2 O·(Fe2 O3) 0 .98铁氧体粉体的矫顽力由未经预烧时的 9.0 395kA·m- 1 线性下降到经 10 0 0℃预烧后的 4.72 46kA·m- 1 。但是 ,饱和磁化强度的变化却是先下降再升高。所获得的Mn0 .6 Cu0 .2 Zn0 .2 O(Fe2 O3) 0 .98纳米晶铁氧体具有较高的矫顽力和饱和磁化强度     

烧结温度对Ca0.4Sr0.6Bi4Ti4O15陶瓷介电性能影响

用固相合成工艺制备Ca<,0.4>Sr<,0.6>Bi<,4>Ti<,4>O<,15>陶瓷材料样品,研究了烧结温度对其介电性能的影响,得出Ca<,0.4>Sr<,0.6>Bi<,4>Ti<,4>O<,15>陶瓷材料最佳的制备工艺.研究结果表明:烧结温度为1210℃,所得样品的晶粒发育较好,介电性能优良,相对介电常数ε<...     

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.     

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).     

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.     

La_(0.2)Sr_(0.8)Co_(0.8)Fe_(0.2)O_(3-z)钙钛矿型混合导电体透氧性能

以稳态法（ＳｔｅａｄｙＳｔａｔｅＰｅｒｍｅａｔｉｏｎＭｅｔｈｏｄ）对Ｌａ０．２Ｓｒ０．８Ｃｏ０．８Ｆｅ０．２Ｏ３－ｚ（ＬＳＣＦ）混合导电体在８５０℃～７００℃间的透氧性能作了测试;同时,以暂态热重法（ＴｒａｎｓｉｅｎｔＴＧＡ）研究了ＬＳＣＦ在８１５℃Ｏ２→Ｎ２→Ｏ２交变气流中的脱氧、吸氧过程,并对其透氧性能作了估算。结果表明,ＬＳＣＦ是一种具有实际应用价值的致密透氧膜;在暂态热重测试条件下,ＬＳＣＦ的吸氧、脱氧过程是可逆的,且整个表面反应受氧脱附过程控制;由暂态热重数据估算出的材料透氧性能比稳态法的推算值低,其值分别为１．５６×１０－７ｍｏｌ／ｃｍ２·ｓ和６４０×１０－６ｍｏｌ／ｃｍ２·ｓ。     

Piezoelectric properties of Ca-modified Pb0.6Bi0.4(Ti0.75Zn0.15Fe0.10)O3 ceramics

Perovskite-structured Pb_0.6Bi_0.4(Ti_0.75Zn_0.15Fe_0.1)O₃ ceramics was reported with high Curie temperature T_C of 705 °C and tetragonality of c/a = 1.10, promising for high temperature applications with large piezoelectric anisotropy. In this paper, it was experimentally demonstrated to ease poling processing and enhance piezoelectricity through substituting lead with calcium of Pb_0.6?xCa_xBi_0.4(Ti_0.75Zn_0.15Fe_0.1)O₃. For the x = 0.18 sample, electromechanical coupling factor ratio of k_t/k_p → ∞, dielectric constant of 380, piezoelectric coefficient d₃₃ of 80 pC/N, mechanical quality factor Q_m of 50 and Curie point T_C of 237 °C were obtained, which exhibits better piezoelectric performance than the (Pb_0.76Ca_0.24)(Ti_0.96(Co_0.5W_0.5)_0.04)O₃. The enhanced piezoelectric response was analyzed with relation to the reduction of tetragonality and Curie temperature.     

Zinc substitution effect on the structural,spectroscopic and electrical properties of nanocrystalline MnFe2O4 spinel ferrite

This paper reports the structural, morphological, spectroscopic, dielectric, ac conductivity, and impedance properties of nanocrystalline Mn_1-xZn_xFe₂O₄. The nanocrystalline Mn–Zn ferrites were synthesized using a solvent-free combustion reaction method. The structural analysis using X-ray diffraction (XRD) pattern reveals the single-phase of all the samples and the Rietveld refined XRD patterns confirmed the cubic-spinel structure. The calculated crystallite size values increase from 8.5 nm to 19.6 nm with the Zn concentration. The surface morphological analysis using field emission scanning electron microscopy and the transmission electron microscopy confirms the nano size of the prepared ferrites. X-ray photoelectron spectroscopy was used to study the ionic state of the atoms present in the samples. Further, the high-resolution Mn 2p, Zn 2p, Fe 2p, and O 1s spectra of Mn_1-xZn_xFe₂O₄ does not result in the appearance of new peaks with Zn content, indicating that the Zn substitution does not change the ionic state of Mn, Zn, Fe, and O present in nanocrystalline Mn_1-xZn_xFe₂O₄. The investigated electrical properties show that the dielectric constant, tan δ and ac conductivity gradually decrease with increasing Zn substitution and the sample Mn_0·2Zn_0·8Fe₂O₄ has the lowest value of conductivity at 303 K. The ac conductivity measured at different temperatures shows the semiconducting nature of the ferrites. The impedance spectra analysis shows that the contribution of grain boundary is higher compared with the grain to the resistance. The obtained results suggest that the Zn substituted manganese ferrite nanoparticles can act as a promising candidate for high-frequency electronic devices applications.     

溶胶-凝胶一步烧结法合成巨介电常数材料CaCu3Ti4O12

通过溶胶-凝胶法合成了巨介电常数材料类钙钛矿型钛酸铜钙(CaCu3Ti4O12,CCTO)先驱物,采用一步烧结法得到纯度较高的CCTO材料。利用X射线衍射、扫描电子显微镜、介电性能测试和阻抗谱测试对样品进行了结构、微观形貌、介电-频率、阻抗谱等分析表征,并讨论了CCTO的微观电导机理和晶粒晶界的性质,计算了晶界活化能。结果表明,此法制备的CCTO样品具有较好的结晶质量、较高的纯度以及优良的介电性能。     

Effect of substrate temperature on structural and electrical properties of BaZr0.2Ti0.8O3 lead-free thin films by pulsed laser deposition

Barium zirconate titanate (BaZr_0.2Ti_0.8O₃, BZT) 250 nm thick thin films were fabricated by pulsed laser deposition and the influence of the substrate temperature on their preferred orientation, microstructure, morphology and dielectric properties was investigated. Dielectric measurements indicated the (1 1 0)-oriented BZT thin films deposited at 750 °C to show good dielectric properties with high dielectric constant (~500 at 100 kHz), low loss tangent (<0.01 at 100 kHz), and superior tunability (>70% at 400 kV/cm), while the largest figure of merit was 78.8. The possible microstructural background responsible for the high dielectric constant and tenability is discussed. In addition, thin films deposited at 750 °C with device quality factor of 8738 and dielectric nonlinearity coefficient of 1.66×10⁻¹⁰ J/C⁴m⁵ were demonstrated.