Microwave absorbing properties of La0.8Ba0.2MnO3 nano-particles

La0.8Ba0.2MnO3 nano-particles were synthesized by sol-gel process, and the crystal structure and morphology＇ were characterized by XRD and SEM, respectively. The complex permittivity and permeability were determined by microwave vector network analyzer in the frequency range of 2-18 GHz. The relationship between reflection coefficient and microwave frequency of La0.8Ba0.2 MnO3 was calculated based on measured data. The results show that the average diameter of La0.8Ba0.2MnO3 crystal powders is about 80 nm and the crystal structure is perovskite when being calcined at 800 ℃ for 2 h. The microwave absorbing peak is 13 dB at 6.7 GHz and the effective absorbing bandwidth above 10 dB reaches 1.8 GHz for the sample with the thickness of 2.6 mm. The microwave absorption can be attributed to both the dielectric loss and the magnetic loss from the loss tangents of the sample, but the former is greater than the latter.     

纳米氧化物La0.8Sr0.2MnO3的制备研究

用添加表面活性剂的苹果酸溶胶凝胶法制备出纳米钙钛石型氧化物La0.8Sr0.2MnO3。通过差热热失重分析,确定了氧化物的焙烧制度。XRD分析表明,所烧制的氧化物样品特征衍射峰明显,杂峰少,晶形完整,其物相为钙钛石结构。表面活性剂因其亲油基团和亲水基团与胶体粒子可以发生复杂的相互作用,形成胶束和胶团,保护了胶体粒子不长大,从而有效地减小氧化物粉料的颗粒粒径,并且在纳米材料的制备过程中能显著降低纳米微粒的表面张力,从而可防止原生粒子团聚,所以在溶胶的制备过程中添加了表面活性剂聚乙烯醇(PVA)。根据谢乐公式计算得出,添加了PVA后,氧化物粉料的粒径约为17nm。TEM分析表明,聚乙烯醇可以作为纳米氧化物粉体La0.8Sr0.2MnO3的分散剂,添加适量的PVA可使纳米粒子的团聚现象得到了明显改善。     

螯合物-凝胶法制备La0.8Sr0.2MnO3粉体

以La(NO3)3·6H2O,Sr(NO3)2和Mn(NO3)3·6H2O为起始原料,采用螯合物-凝胶法制备出La0.8Sr0.2MnO3粉体.首先在混合盐溶液中入柠檬酸形成螯合的柠檬酸盐,然后加入单体和交联剂,在引发剂和催化剂的作用下形成湿凝胶.干燥后的前驱体为无定形的,DTA和XRD测试表明晶化温度在400℃～500℃.在500℃～1 200℃范围内煅烧,颗粒尺寸由500℃时的约38 nm 长大到1 200℃时的500 nm.     

凝胶注模制备La0．8Sr0．2MnO3多孔阴极材料

采用凝胶注模技术原位合成造孔剂制备出开孔气孔率为20％～30％的La0．8Sr0．2MnO3多孔阴极材料。结果表明，合适的烧结温度为l100℃～1150℃；开口气孔位于三角晶界，中位孔径约为400nm；多孔材料的电导率随着温度的升高而升高，由ln(σT)-1／T曲线，可得电导活化能Ea为10．99kJ／mol。     

Molten salt synthesis of La0.8Sr0.2MnO3 powders for SOFC cathode electrode

For La_0.8Sr_0.2MnO₃ (LSM) perovskite, used as the cathode material for solid oxide fuel cells (SOFC), it is known that the formation of a triple-phase-boundary is restrained due to the formation of a second phase at the YSZ/electrode interface at high temperature. To decrease the 2^nd phase, lowering the sintering temperature has been used. LSM powder was synthesized by molten salt synthesis method to control its particle size, shape, and agglomeration. We have characterized the phase formation, particle size, shape, and sintering behavior of LSM in the synthesis using the variation of KCl, LiCl, KF and its mixed salts as raw materials. In the case of KCl and KCl-KF salts, the particle size and shape of the LSM was well controlled and synthesized. However, in the case of LiCl and KCl-LiCl salts, LiMnO_x as 2^nd phase and LSM were synthesized simultaneously. In the case of the mixed salt of KCl-KF, the growth mechanism of the LSM particle was changed from ‘diffusion-controlled’ to ‘reaction-controlled’ according to the amount of mixed salt. The sintering temperature can be decreased below 1000 °C by using the synthesized LSM powder.     

Fabrication and performance of La0.8Sr0.2MnO3/YSZ graded composite cathodes for SOFC

The performance of multi-layer (1-x)La0.8Sr0.2MnO3/xYSZ graded composite cathodes was studied as electrode materials for intermediate solid oxide fuel cells (SOFC). The thermal expansion coefficient, electrical conductivity, and electrochemical performance of multi-layer composite cathodes were investigated. The thermal expansion coefficient and electrical conductivity decreased with the increase in YSZ content. The (1-x)La0.8Sr0.2MnO3/xYSZ composite cathode greatly increased the length of the active triple phase boundary line (TPBL) among electrode, electrolyte, and gas phase, leading to a decrease in polarization resistance and an increase in polarization current density. The polarization current density of the triple-layer graded composite cathode (0.77 A/cm2) was the highest and that of the monolayer cathode (0.13 A/cm2) was the lowest. The polarization resistance (Rp) of the triple-layer graded composite cathode was only 0.182Ω·cm2 and that of the monolayer composite cathode was 0.323Ω·cm2. The power density of the triple-layer graded composite cathode was the highest and that of the monolayer composite cathode was the lowest. The triple-layer graded composite cathode had superior performance.     

Microstructure and Electrochemical Behavior of La0.8Sr0.2MnO3 Deposited by Solution Precursor Plasma Spraying

采用液料等离子喷涂方法(SPPS)制备固体氧化物燃料电池多孔La0.8Sr0.2MnO3(LSM)阴极。用SEM观察LSM的微结构,用XRD研究其相结构。考察了喷涂距离和热处理温度对LSM微结构的影响规律。结果表明,SPPSLSM在1050℃热处理2h后形成连续的具有微纳介孔结构的涂层,且LSM具有单一的钙钛矿结构。利用电化学交流阻抗谱方法研究了LSM极化行为。微结构对极化性能有显著影响,1000℃时,LSM在喷涂距离为60mm时具有最佳的电化学性能,阴极极化电阻约为0.3Ω·cm2。通过工艺的控制,SPPS可以实现SOFC阴极相和微结构的优化。     

Preparation and characterization of La0.8Cu0.2MnO(3±δ) perovskite-type catalyst for methane combustion

La0.8 Cu0.2 MnO(3±δ) perovskite-type catalyst for methane combustion prepared through sol-gel process was characterized by X-ray Diffractometry(XRD), X-ray Photoelectron Spectroscopy(XPS) and Scanning Electron Microscopy(SEM). XPS analyses reveal that the surface characteristics of the catalyst are changed. The lattice defects and oxygen vacancies on the catalyst surface are enhanced due to a part of La3+ being substituted by Cu2+.Temperature-programmed-desorption(TPD) and temperature-programmed-reduction(TPR) analyses were carried out to study the catalytic behavior. It is found that there are two O2-desorption peaks at 350 ℃ and 650 ℃ in the TPD pattern, and two CH4-consumption peaks at 420 ℃ and 750 ℃ in the TPR patterns respectively, which indicates that the two kinds of oxygen species, so-called α and β oxygen, can react with the methane during catalytic combustion process. The catalytic activity tests were performed in a fixed-bed reactor, and the results show that the T1/2 at which the conversion of methane attains 50 % of La0.8 Cu0.2 MnO(3±δ) is lower by 55 ℃ than that of LaMnO3.This indicates that the catalytic activity of La0.8 Cu0. 2 MnO(3±δ) is increased with partial substitution of Cu2+ for La3+.     

A facile synthesis of TiB2 nano-particles via mechano-thermal route

A mixture of TiO₂, B₂O₃ and Si powders was milled up to 50 h using a high energy planetary ball mill. The milling products were heat treated at 850, 1200 and 1300 °C. Effects of Si content and addition of catalyst on the phase evolutions and morphology of the products were investigated. XRD results showed that phase composition of the 50 h milled sample after heat treatment at 1300 °C consists of nano-crystalline TiB₂ with mean crystallite size of 50 nm together with some Ti₂O₃, Si and SiO₂ phases. Addition of 2 mol of NaCl in the same sample facilitates the process and resulted in the single phase TiB₂with a mean crystallite size of 30 nm. SEM and TEM micrographs exhibited the nano-sized particles of TiB₂.     

Synthesis and on-line ultrasonic characterisation of bulk and nanocrystalline La0.68Sr0.32MnO3 perovskite manganite

La_0.68Sr_0.32MnO₃ perovskite manganite samples were prepared using sonochemical reactor and solid state reaction technique. The ultrasonic velocity, attenuation and elastic moduli of samples were measured using ultrasonic through transmission method, at a fundamental frequency of 5 MHz over a wide range of temperatures. The temperature dependence of the ultrasonic parameters shows an interesting anomaly in all the compositions. The observed dramatic softening and hardening in sound velocities or attenuation is related to phase transitions. The linear magnetostriction effect is more dominant in the perovskite than volume magnetostriction effect which is evident from the observed anomalous in both longitudinal and shear velocities and attenuation. Further, a decrease in grain size in the sintered sample leads to a shift in the ferromagnetic transition temperature (T_C) from 375 to 370 K.     

溶胶-凝胶法制备La0.8Sr0.2CoO3纳米材料

以La(NO3)3·6H2O、Sr(NO3)2、Co(NO3)2·6H2O为原料,用EDTA络合溶胶-凝胶法制备La0.8Sr0.2CoO3凝胶,在700℃、800℃、900℃煅烧,制得La0.8Sr0.2CoO3粉体.用DTA、FT-IR、XRD、SEM等手段对制备过程、热分解机理及粉体的性能进行了研究.在700℃焙烧2 h得到La0.8Sr0.2CoO3纯相纳米粉,颗粒呈球形.选取700℃焙烧2 h的La0.8Sr0.2CoO3粉体制成管状传感器,进行NO2敏感性能测试,探讨了相同NO2浓度下,传感器敏感信号与温度的关系.结果表明:纳米La0.8Sr0.2CoO3粉体在450℃时对NO2的敏感信号最大,输出的电动势信号与NO2浓度之间呈线性关系.     

微波辅助溶胶凝胶法合成La0.8Sr0.2Co0.5Fe0.5O3阴极材料及性能研究

使用一种新的理想方法--微波辅助溶胶凝胶法,在35 min内快速制备了钙钛矿结构的La0.8Sr0.2Co0.5Fe0.5O3(LSCF)纳米材料;以8%Y2O3稳定化的ZrO2(YSZ)为电解质,La0.8Sr0.2Co0.5Fe0.5O3为阴极,铂电极为阳极,制备了LSCF/YSZ/Pt固体氧化物电池.采用X射线粉末衍射(XRD)、傅里叶红外光谱(FT-IR)、扫描电子显微镜(SEM)、BET和电化学阻抗谱(EIS)等技术研究了La0.8Sr0.2Co0.5Fe0.5O3材料的成相过程、粉晶结构、电极/电解质微观相貌和电池电化学性能.结果发现经过1 min的微波辐射,凝胶开始分解,3 min后有钙钛矿相生成,到35 min时形成了完整的钙钛矿晶相,相应粉体的粒径和比表面积分别为22.7 nm和38.9 m2/g;在1094 K,0 mV偏置电压下电极/电解质界面电阻为0.775 Ω·cm2,活化能为2.34 eV.研究发现,偏置电压越大则活化能越低.     

纳米晶La0．8Sr0．2FeO3气敏元器件的制备与乙醇敏感特性

采用溶胶-凝胶法制备了纳米晶La0.8Sr0.2FeO3。X射线衍射表明：该样品为正交晶系钙钛矿结构，其平均粒径约为31nm。将La0.8Sr0.2FeO3纳米晶粉体与聚乙烯醇PVA混合固化，然后在400℃下分别退火20min和120min。固化退火120min的元器件电阻随乙醇浓度的增加而增加，元器件具有P型半导体特性。而固化退火20min的元器件电阻随乙醇浓度的增加而减小，该元器件具有n型半导体特点。固化退火120min的La0．8Sr0．2FeO3元器件的气敏灵敏度S=Rg／Ra在80℃下高达100，低工作温度、高灵敏度特性对应用有益。发现La0.8Sr0.2FeO3元器件的电阻R和乙醇浓度C只在较低温区符合指数关系（R≈KC^α）。     

高温质子导体Ba(Ce0.8Zr0.2)0.9Y0.1O3-δ的合成与性能

采用低温燃烧法合成掺Zr的新型高温质子导体Ba（Ce0.8 Zr0.2）0.9Y0.1O3-δ陶瓷粉体。运用X射线衍射仪、扫描电子显微镜以及激光粒度仪分别对粉体的晶型、微观形貌和粒度分布进行分析。通过控制柠檬酸用量与金属离子摩尔总量的比，直接制备出具有斜方晶钙钛矿结构的纯Ba（Ce0.8 Zr0.2）0.9Y0.1O3-δ超细粉体，且粉体粒度分布均匀，平均粒径为5．55μm。粉体烧结性能实验结果表明，粉体在1200℃发生烧结，在1300℃下烧结致密，相对密度达到94．32％。     

Preparation and magnetic properties of nanosized （La0. 47Gd0. 2 ） Sr0. 33 MnO3

1INTRODUCTION Themagneticpropertyandcrystalstructureof perovskite typelanthanummanganeseoxideswere firststudiedbyJonkerandVanSantenin1950[1].Thesematerialswereofconsiderableinterestinthe lastdecadeduetotheircolossalmagnetoresistance(CMR)effect[24].Recentlyaseriesofhole dopedperovskitemanganeseoxideswerereportedtodis playalargemagnetocaloriceffect(MCE)inthevic inityoftheferromagneticCurietemperature(Tc)[516],whichmaybeexploitedtobeappliedin magneticrefrigeratorandheatpumps[17].Idealmag…     

共沉淀法合成新型阴极材料Ba0.5Sr0.5Co0.8Fe0.2O3-σ

草酸共沉淀法合成了中温固体氧化物燃料电池（ITSOFC）新型阴极材料Ba0.5Sr0.5Co0.8Fe0.2O3-σ（BSCF）。XRD，DSC和SEM结果显示：经过900℃煅烧2h后，产物的钙钛矿结构已经初步形成，但由于晶化不完全，衍射峰强度相对较弱，且存在杂相；随着煅烧温度提高到1200℃后，产物中杂相消失，晶体结构转变为单一的立方型钙钛矿，颗粒大小基本在2μm～3μm；BSCF与Ce0．8Sm0．2O1．9（SDC）混合物（质量比1：1）在1000℃下热处理24h后未发现杂相，表明BSCF与SDC具有良好的化学相容性。     

La_（0.85）K_（0.15）MnO_3多晶纳米颗粒磁制冷材料的制备

采用非晶态多核配合的方法在800℃制备出La0.85K0.15MnO3纳米颗粒,用XRD、HRTEM和PPMS等手段对纳米颗粒的微观结构和磁性能进行研究。XRD和ED分析表明,所有样品都具有单相钙钛矿结构;样品的M-T曲线研究结果表明,La0.85K0.15MnO3纳米颗粒的居里温度TC为242.65 K。     

La0．8Ca0．2CrO3钙钛矿复合氧化物的GNP法合成与表征

采用GNP（Glycine-Nitrate Process）法合成La0.8Ca0.2CrO3初级粉料，研究甘氨酸用量对产物的晶体结构和显微形貌的影响，并测试烧结体的相对密度和电导率。研究结果表明，甘氨酸与金属离子的摩尔比（G／M^n＋）控制在2．0～2．5时可得到颗粒尺寸细小、均匀（100nm～200nm）的单相钙钛矿粉体，烧结温度为1350℃时样品的相对密度达到91．0％，测试温度为800℃时样品的电导率达到30．5S.cm^-1。与常规固相法相比，GNP法制备的样品具有更好的烧结活性和导电性能。     

La0.8Sr0.2 Mn1-yFeyO3微波电磁特性与损耗机制

用溶胶凝胶法制备La0.8Sr0.2Mn1-yFeyO3(y=0.10,0.12,0.14,0.16)样品,测试并分析该样品在2~18 GHz微波频率范围的复介电常数、复磁导率、损耗角正切及微波吸收系数与频率的关系,发现y=0.12,0.14时吸波的效果最好。样品厚度为2 mm、y为0.12时,有2个吸收峰,吸收峰值最高达22 dB,10 dB以上吸收频带宽度达6.2 GHz;厚度2.21 mm样品8 dB以上的吸收频宽达8.5 GHz。初步探讨了该材料的电磁损耗机理,电磁特性参数在频率为12.4 GHz位置发生阶跃式变化,在小于12.4 GHz频率范围以介电损耗为主,在大于12.4 GHz频率范围以磁损耗为主,这与Fe对Mn3 —O—Mn4 之间的影响有关。电导率测试表明在室温范围内电导在半导体范围内,有利于降低微波在氧化物表面的反射率。     

低温燃烧合成La0.9Sr0.1Ga0.8Mg0.2O2．85固体电解质粉末

低温燃烧合成工艺结合了溶液法和高温自蔓延合成超细粉末工艺的特点，可以在较低的温度下引发化学反应，并利用反应自身的放热效应维持反应的继续进行。在硝酸盐．柠檬酸体系中用该工艺直接合成了比表面积超过120m^2／g的La0.9Sr0.1Ga0.8Mg0.2O2.85固体电解质超细粉末。研究了硝酸盐溶液起始浓度和pH值对产物性能的影响。