La3+掺杂对(Sr,Ba,Ca)TiO3基压敏陶瓷结构和性能的影响

采用常规固相法制备(Sr,Ba,Ca)TiO3基压敏陶瓷.用Nb5 离子取代Ti4 离子,Mn作受主掺杂元素的前提下,系统研究了稀土离子La3 施主掺杂对压敏陶瓷结构和性能的影响.结果表明,当La2O3=0.4%(摩尔分数)时,(Sr,Ba,Ca)TiO3基压敏陶瓷可获得良好的电性能:其压敏电压V10mA=11.19V,非线性系数α=2.93,电容C=31.16nF,介电损耗tanδ=0.43%,压敏电压温度系数KV10mA=0.1%/℃.     

改性(Sr,Ca)TiO3基储能陶瓷介电及MLCC性能研究

工业级脉冲储能多层瓷介电容器(MLCC)是现阶段国内研制和生产电子启动装置的重要元器件, 针对国内主要有机薄膜电容器尺寸大、寿命短、可靠性较低的不足, 本研究采用传统固相反应法, 制备了SrTiO₃和CaTiO₃基的脉冲储能介质陶瓷材料, 研究了微量助烧剂掺杂, 以及Sr²⁺/Ca²⁺相互掺杂对陶瓷材料的介电性能的影响, 并进一步制备和研究了以(Sr,Ca)TiO₃为基体MLCC性能。实验结果表明: 通过加入质量分数1.0%的助烧剂, 引入微量Bi³⁺ 可取代Sr²⁺, 提高了SrTiO₃材料的介电常数, 而Bi³⁺对CaTiO₃基材料的介电性能无明显影响; Mn元素有效抑制高温烧结中Ti⁴⁺的还原, 降低介电损耗; 加入助烧剂有效降低瓷粉的烧结温度, 提高材料的致密性。(Sr_xCa_1-x)TiO₃体系的MLCC可保持较高的介电常数和较低的介电损耗, 当 x=0.4 时, 其介电损耗tanδ=1.8×10^-4, 击穿强度为59.38 V/μm, 高低温放电电流变化率为±7%, 放电稳定, 在常温和高温(125 ℃)下经1000次循环充放电实验均未失效, 是一种在不同电场强度下具有相对较优的容量稳定性以及较高可靠性的脉冲特性(Sr,Ca)TiO₃基电容器陶瓷介质材料。     

(La0.9Bi0.1)2/3Ca1/3MnO3磁性和电输运性质研究

利用固相反应法制备了(La0.9Bi0.1)2/3Ca1/3MnO3样品,研究了它的导电特性和磁性.在电阻和磁化测量中观察到热滞现象. 在电阻-温度(R-T)曲线中出现了两个峰,当施加5T外场时,电阻中的热滞现象被抑制,只观察到一个峰.磁化(M-T)曲线表明,在居里温度(Tc)以下发生了顺磁-铁磁(PM-FM)相变. 样品不同寻常的M-T行为能够很好地解释测量到的R-T曲线.     

钙钛矿型复合氧化物La1-xSrxFe1-yCoyO3的制备与应用

综述了钙钛矿型复合氧化物La1-xSrxFe1-7CoyO3的制备方法，介绍了其结构，性能特征及其主要应用前景。     

La0.6M0.4Fe0.8Cr0.2O3-δ(M=Ca、Sr、Ba)的制备、表征及电性能

采用甘氨酸-硝酸盐法(GNP)制备了纳米尺寸的La0.6M0.4Fe0.8Cr0.2O3-δ(M=Ca、Sr、Ba)系列粉体.BET测试表明,合成粉体的比表面积>20m2·g-1;XRD结果显示,GNP法合成粉体在燃烧阶段物相已初步形成,La0.6Ca0.4Fe0.8Cr0.2O3-δ(LCFC)初粉经850℃热处理2h即转变为简单立方钙钛矿结构的纯相产物,1100℃下烧结体的相对密度即达95%,La0,6Sr0.4Fe0.8Cr0.2O3-δ(LSFC)、La0.6Ba0.4Fe0.8Cr0.2O3-δ(LBFC)初粉为双相结构,两者在低温段的烧结活性较LCFC差,1300℃以上相对密度接近95%.四端子法电导测试表明,掺杂样品的电导率较LaFeO3高2个数量级以上,700℃以下三者的电导率随温度的变化符合小极化子导电机理;800℃下LCFC的电导率>50S·cm-1,预示其可能成为IT-SOFC有实际应用前景的阴极材料.     

La0.6Sr0.4Co1-yFeyO3系阴极材料制备及表征

La1-xSrxCo1-yFeyO3系(LSCF)钙钛矿结构氧化物是一类性能优异的离子-电子混合导体,同时具有良好的化学稳定性和催化活性,有望作为中低温条件下工作的固体氧化物燃料电池阴极材料的候选材料.本文采用固相反应法制备了多孔La0.6Sr0.4Co1-yFeyO3(y=0.2～0.8)氧化物陶瓷,通过XRD,TG/DTA等测试技术研究了LSCF的结构与制备过程,采用直流四探针法测试了样品的电导率,同时考察了这类组成样品的热膨胀系数.结果表明,这类组成的电导率都有着相同的变化趋势,即先随温度升高而增大,至极大值后又开始降低.分析表明,除了存在小极化子导电机制外,同时还可能存在以下几种机理:1)热激发引起Co3 离子的电荷歧化;2)高温下氧空位生成导致的离子补偿;3)Fe4 较Co4 优先进行电子补偿.     

La0.8Sr0.2CoxFe1-xO3型氧扩散障层材料的制备及结构性能研究

采用共沉淀-凝胶方法制备La0.8Sr0.2CoxFe1-xO3(x=1.0、0、0.3)氧扩散障碍层材料的前驱体,分别用X射线衍射分析、透射电镜、扫描电镜和交流阻抗谱仪对三种不同粉体及其陶瓷结构和性能进行研究.结果表明:在870℃下焙烧制备的La0.8Sr0.2CoxFe1-xO3(x=1.0、0、0.3)粉末具有钙钛矿相结构,无硬团聚,颗粒大小在20～60 nm.此粉末经冷等静压250MPa成型后,在1120℃下烧结6h,La0.8Sr0.2CoO3和La0.8Sr0.2FeO3混合导体的电导率在10—1S/cm数量级,而La0.8Sr0.2Co0.3Fe0.7O3导电率最高达100 S/cm数量级.三种陶瓷都是电子电导远大于离子电导的混合导体,电导率最高值在200～300℃范围,偏向低温.     

不同厚度的La2/3Sr1/3MnO3多晶薄膜输运性质研究

运用磁控溅射的方法,在表面氧化的Si(100)基片上制备了一系列不同厚度的La2/3Sri/3MnO3多晶薄膜.根据对输运的研究,发现存在一个厚度73nm,当t＞73nm的时候,薄膜呈现出与块材类似的输运特点,而当t＜73nm的时候,薄膜的电阻太大以至于薄膜的金属-绝缘体转变温度(Tp)变得不可测量.X射线衍射(XRD)结果显示:在t=73nm附近存在一个结构的转变.这表明La2/3Sr1/3MnO3不同厚度多晶薄膜的输运性质的不同或许来自结构的转变.     

La0.6M0.4Fe0.8Cr0.2O3-δ(M=Ca、Sr、Ba)的制备表征及电性能

采用甘氨酸-硝酸盐法(GNP)制备了纳米尺寸的La0.6M0.4Fe0.8Cr0.2O3-δ(M=Ca、Sr、Ba)系列粉体.BET测试表明,合成粉体的比表面积＞20 m2·g-1;XRD结果显示,GNP法合成粉体在燃烧阶段物相已初步形成,La0.6Ca0.4Fe0.8Cr0.2O3-δ(LCFC)初粉经850℃热处理2h即转变为简单立方钙钛矿结构的纯相产物,1100℃下烧结体的相对密度即达95%,La0.6Sr0.4Fe0.8Cr0.2O3-δ(LSFC)、La0.6Ba0.4Fe0.8Cr0.2O3-δ(LBFC)初粉为双相结构,两者在低温段的烧结活性较LCFC差,1300℃以上相对密度接近95%.四端子法电导测试表明,掺杂样品的电导率较LaFeO3高2个数量级以上,700℃以下三者的电导率随温度的变化符合小极化子导电机理;800℃下LCFC的电导率＞50 S·cm-1,预示其可能成为IT-SOFC有实际应用前景的阴极材料.     

高温燃料电池阴极材料La（Sr）MnO3的电导性能研究

用固相合成法合成了（Ｌａ１－ｘＳｒｘ）１－ｙＭｎＯ３（ｘ＝０～５，ｙ＝０～０．１）单纯相化合物。在空气中用直流四探针法测定了各组成的电导率。测试温度范围为１００～９５０℃。其中（Ｌａ０．７Ｓｒ０．３）０．９５ＭｎＯ３具有最大的电导率。讨论了Ｌａ（Ｓｒ）ＭｎＯ３的电导机理。     

钙钛矿型复合氧化物MZrO3（M=Ba,Sr）的水热合成

利用水热晶化法对ＢａＺｒＯ３和ＳｒＺｒＯ３的制备进行了研究，对不同水热条件下的产物进行了结构表征，并探讨了最佳合成条件，结果表明，１５０℃，晶化１ｄ为最佳水热晶化条件，介质的适宜碱度为ＫＯＨ／Ｚｒ≈４。在此条件下，可获得３－７μｍＢａＺｒＯ３和５－１５μｍＳｒＺｒＯ３的多晶粉末。     

Microstructure and properties of (Sr,Ca)CuO2/(Sr,Ca)RuO3 multilayers

Epitaxial multilayer thin films of “infinite-layer” (Sr, Ca)CuO₂ and perovskite (Sr, Ca)RuO₃ have been prepared on (100) SrTiO₃ substrates by multitarget rf magnetron sputtering. X-ray diffraction analyses revealed that the multilayer structure of (Sr, Ca)CuO₃/(Sr, Ca)RuO₃ was successfully fabricated with a minimum layer thickness of 20 Å. Transmission electron microscopy measurements of the multilayers indicated that there was no dislocation which normally exists in single-layer films with an infinite-layer structure. Resistivities of multilayer films at room temperature ranged from 1 to 10 mΩ cm and showed semiconductor-like dependence against the temperature.     

Electrical properties of (Ba,Sr)TiO3 on (Sr,Ca)RuO3 electrode

A perovskite (Sr,Ca)RuO₃ [SCR] electrode has been explored in order to utilize its advantages in structural match with (Ba,Sr)TiO₃ [BST] films, which may enhance the electrical properties of BST films. The SCR electrode led to the leakage current density (10^–7 A/cm²) of BST films an order lower than that on RuO₂. The leakage current was not sensitive to the composition of the SCR electrodes, while the dielectric constant of the BST thin film capacitor ranged from 160 to 280 depending on the Sr/Ca ratio in SCR electrodes. The BST/SCR (Sr/Ca = 7/3) system resulted in a 5–nm thick interfacial layer. Furthermore, the interfacial layer turned out to be partially crystallized according to the lattice image taken by an HRTEM. It is believed that such enhancement in electrical properties of BST films could be induced by the improvement of interfacial characteristics through structural matching.     

(Ca,Sr,Ba)3V2O8的制备和发光性能研究

采用微波辅助溶胶-凝胶法制备了自激发钒酸盐A3(VO4)2(A:Ca,Sr,Ba)。采用X射线衍射仪、傅里叶变换红外光谱仪、扫描电镜、透射电子显微镜、荧光谱仪对样品各项参数进行了表征,研究了A3(VO4)2的光致发光特性,探讨了不同制备工艺条件对其发光性质的影响。实验结果表明,Sr3V2O8样品发光强度随退火温度而变化,在680～900℃时,其发射光谱强度随温度上升而单调下降,达到1000℃时开始上升;pH值为4时,样品的发射光谱强度最大。     

Composition dependent intrinsic defect structures in ASnO_3(A=Ca,Sr,Ba)

Perovskite stannates are promising semiconductors that are widely used in optoelectronic devices.Here,the composition dependent intrinsic point defects of stannate perovskites ASnO_3(A=Ca,Sr,Ba) are studied by first-principles calculations.The prefe rences of de fects under stoichiometric and nonstoichiometric conditions are unsealed,meanwhile the charge states of each intrinsic defect varying with the change of electron Fermi energy are clarified.For stoichiometric BaSnO_3 and SrSnO_3,the Schottky defect complexes are predicted as the most stable defect structure,while the antisite defect complexes are the most stable one in CaSnO_3.In nonstoichiometric ASnO_3,excessive AO is beneficial to the formation of oxygen vacancies and A-Sn antisite defects in all ASnO_3;while the Ca interstitial is another major defect existing in CaSnO_3.In the case of SnO_2 excess,the predominant de fects are the Sn-A antisite defects and A vacancies.Since the functionality of these perovskite oxides is closely related to the types and concentrations of their point defects,the present results are expected to guide the future experiments to optimize the function of the perovskite oxides by tailoring the intrinsic defects through controlling the composition of AO and SnO_2.     

白光LED用红色荧光粉MMoO4:Eu3+（M=Ca,Sr,Ba）的制备与表征

采用高温固相法制备了红色荧光粉MMoO4:Eu3+(M=Ca,Sr,Ba),用XRD和荧光分光光度计对其物相及发光性能进行表征和研究。结果表明,在800℃时可得到MMoO4(M=Ca,Sr,Ba)物相结构。分别以395nm的近紫外光和465nm的可见光激发样品,MMoO4:Eu3+(M=Ca,Sr,Ba)荧光粉发红光,对应于Eu3+的4f-4f跃迁,其中以616nm发光最强。荧光粉在395nm和465nm的吸收分别与紫外光和蓝光LED芯片相匹配。     

Preparation, characterization, and magnetic studies of Bi0.5X0.5(X = Ca, Sr)MnO nanoparticles

Nanoparticles (dia. approximately 5-7 nm) of Bi0.5X0.5(X = Ca, Sr)MnO3 are prepared by polymer assisted sol-gel method and characterized by various physico-chemical techniques. X-ray diffraction gives evidence for single phasic nature of the materials as well as their structures. Mono-dispersed to a large extent, isolated nanoparticles are seen in the transmission electron micrographs. High resolution electron microscopy shows the crystalline nature of the nanoparticles. Superconducting quantum interferometer based magnetic measurements from 10 K to 300 K show that these nanomanganites retain the charge ordering nature unlike Pr and Nd based nanomanganites. The CO in Bi based manganites is thus found to be very robust consistent with the observation that magnetic fields of the order of 130 T are necessary to melt the CO in these compounds. These results are supported by electron magnetic resonance measurements.     

A structural study on MFCl (M=Ca, Sr, Ba) and BaFX (X=Br, I)

Here we present the electronic band structure calculations of CaFCl, SrFCl, BaFCl, BaFBr and BaFI performed using tight binding linear muffin-tin orbital method. The calculated ground state properties namely the lattice parameters, bulk moduli and the pressure-volume relations were found to be in good agreement with the experimental values. The electronic band structure of these compounds were calculated at ambient as well as in the high pressure region. The band gap values of these insulating systems were calculated and compared with available experimental values. At high pressure these compounds exhibit the interesting phenomenon of band overlap metallization.     

Preparation of hydroxyapatites via the MSO4 sulphates (M = Ca,Sr, Pb and Eu)

Hydroxyapatites of Ca, Sr and Pb have been prepared by a reaction of the sulphates of these metals with sodium phosphate arsenate or vanadate respectively in a strongly basic solution. X-ray diffraction and IR spectroscopy proved the formation of hydroxyapatites. DTA and TG data indicate the presence of one water molecule in Ca₅(PO₄)₃OH lost at 110°C.     

Phase evolution and microstructural development in sol-gel derived MSnO3 (M = Ca, Sr and Ba)

Alkaline-earth stannates having the general chemical formula MSnO₃ (M = Ca, Sr and Ba) have been projected as potential electronic ceramics. In view of the information gaps in the reported research, a vigorous and systematic investigation on these exotic materials has been carried out. In this communication, the synthesis of CaSnO₃, SrSnO₃ and BaSnO₃ via sol-gel technique is reported. Infrared spectroscopy and X-ray analyses of various gel samples with different thermal history helped in identifying the reaction pathways and the stage where amorphous gel to crystalline phase transition occurred. Grains of submicron size with narrow size distribution and spherical morphology, were the most noticeable characteristics of sintered calcium metastannate derived by sol-gel method. In the case of barium analogue, a fascinating sugar cube structure (akin to that observed in solid-state reaction and the self-heat-sustained reaction derived samples) having improved density characteristics evolved at low sintering temperatures. This gradually transformed into a more familiar spherical granular motif with improved density characteristics as the sintering profiles were varied from 1200 °C/24 h to 1500 °C/2 h. This seems to be an inherent feature of this system, irrespective of the method of synthesis.