调节带宽对钙钛矿锰氧化物电荷有序相的影响

用固相法制备了Pr0.45(Ca1-xSrx)0.55MnO3(x=0,0.2,0.4,0.6,0.8,1.0)多晶样品.通过X射线衍射谱、磁化强度-温度曲线、电子自旋共振谱研究了Sr2+替代Ca2+对Pr0.45(Ca1-xSrx)0.55MnO3体系电荷有序(charge ordering,CO)相的影响,结果表明...     

La0.3Ca0.7Mn1-xVxO3体系的电荷序和自旋序

通过对样品La0.3Ca0.7Mn1-xVxO3(x=0.05,0.10,0.134,0.20)的磁化强度-温度(magnetization-temperature, M-T)曲线、电阻率-温度(resistivity-temperature, p-T)曲线、电子自旋共振谱的测量,研究了Mn位V掺杂La0.3Ca0.7MnO3体系电荷序和自旋序的影响.结果表明:当0.05≤x≤0.134时,体系存在电荷有序(CO)相,体系自旋序随温度降低发生顺磁(paramagnetism, PM)-荷有序(charge ordering, CO)-反铁磁(antiferromagnetism, AFM)变化.当x=0.20时,电荷有序融化,体系出现再入型自旋玻璃行为.     

La0.7Ca0.3MnO3纳米颗粒的聚丙烯酰胺凝胶法制备及性能

采用聚丙烯酰胺凝胶法制备La0.7Ca0.3MnO3纳米颗粒。通过X射线衍射和扫描电镜研究不同pH值和不同络合剂对制备La0.7Ca0.3MnO3纳米颗粒形貌及性能的影响。结果表明：合成La0.7Ca0.3MnO3钙钛矿相的最佳pH=2;分别以醋酸、草酸、柠檬酸和乙二胺四乙酸为络合剂,在600℃煅烧温度制备的高纯La0...     

La（0.3）Ca（0.7）Mn（1–x）VxO3体系的电荷序和自旋序（英文）

通过对样品La0.3Ca0.7Mn1–xVxO3（x=0.05,0.10,0.134,0.20）的磁化强度–温度（magnetization–temperature,M–T）曲线、电阻率–温度（resistivity–temperature,ρ–T）曲线、电子自旋共振谱的测量,研究了Mn位V掺杂对La0.3Ca0.7MnO3体系电荷序和自旋序的影响。结果表明：当0.05≤x≤0.134时,体系存在电荷有序（CO）相,体系自旋序随温度降低发生顺磁（paramagnetism,PM）–电荷有序（charge ordering,CO）–反铁磁（antiferromagnetism,AFM）变化。当x=0.20时,电荷有序融化,体系出现再入型自旋玻璃行为。     

复合掺杂钙钛矿氧化物La0.6Sr0.4-xCaxCo1-yNiyO3-δ阴极的制备和电性能

采用固相反应法合成了中温固体氧化物燃料电池新型复合掺杂阴极La0.6Sr0.4-xCaxCo1-yNiyO3-δ（LSCCN）钙钛矿材料。借助XRD对不同掺杂含量所制备的粉体的成相过程和晶体结构进行了研究。实验结果表明：当x=0.4时,Ca元素已经不能很好的掺入到LaCoO3晶格中去。Ni元素含量较小的情况下,不会影响材料的晶体结构,不过当NiO含量稍有增高,制备的粉体的结构发生了明显的变化,已不再具有钙钛矿型的晶体结构,出现了较强的四方K2NiF4结构的LaSrCoO4衍射峰。将制备的LSCCN粉体掺入一定的淀粉和粘结剂制备成固体氧化物燃料电池（SOFC）的阴极。在空气气氛下使用直流四探针法测量了样品从100℃到800℃的电导率值,发现LSCCN系列材料中保持了钙钛矿结构的阴极片具有很高的电导率值,其中Ca2+和Sr2+掺杂各半的情况下制备的阴极片的电导率值最高。掺入较多的Ca2+或较多的Ni2+不仅影响了材料的单一的晶体结构,并且大大降低了材料的电导率值。     

掺杂离子的种类对介孔La0.6A0.4NiO3钙钛矿催化剂的结构与催化活性的影响

以十六烷基三甲基溴化铵（CTAB）为模板剂,用共沉淀法分别制备了介孔La_0.6A_0.4NiO₃（A=Ce、Sr、Y、Nd、Pr）钙钛矿复合氧化物,用XRD、SEM、FTIR、BET和程序升温技术等对复合氧化物的晶相结构、表面形貌、表面积、孔径分布及表面性能等进行了表征,同时在蔗渣高压液化反应中探讨了A位离子掺杂种类对介孔La_0.6A_0.4NiO₃催化活性和液化产物分布及液化油含量的影响。结果表明,掺杂的A位离子均能进行不同程度的同晶取代,其中掺杂的Pr³⁺能较好的与La³⁺发生同晶取代,且具有较大的比表面积和孔径分布,表面存在较强的氧物种传导性和碱性中心,在蔗渣高压液化反应中具有较高的液化油产率和较低的残渣率,生物质油的主要成分为乙酰柠檬酸三丁酯、柠檬酸三正丁酯、对乙基苯酚、6-乙基-3-肽酸酯,有利于提高油品的质量。     

钛掺杂对于YMnO3多铁性能的调控

利用固相反应法制备了钛掺杂的YMn_(1–x)Ti_xO_3 (x=0.1,0.2)固溶体,对掺杂前后体系的晶格结构、磁性以及铁电性进行了研究。结果表明:掺杂后的样品仍然维持六角相结构,在x=0.2时开始有菱形■结构出现,掺杂体系保持着原有的铁电与反铁磁共存的状态,并伴随着弱铁磁性的出现;随着掺杂的增加由Curie-Weiss拟合得到的Weiss温度(负值)逐渐升高,表明反铁磁作用在减弱;体系在低温会发生自旋玻璃态转变,同时冻结温度Tf随着掺杂量的增加逐渐降低;对于体系铁电性测量表明其依然保留着原有的铁电性能,且极化强度会随着掺杂浓度的提高而增强。     

Mn掺杂对La0.5Ca0.5MnxTi1-xO3介电行为的影响

利用传统的固相烧结方法,成功制备了La和ca,Mn和Ti相互替代的正交钙钛矿相La0.5Ca0.5MnxTi1-xO3(0≤x≤0.6)陶瓷。通过X射线衍射,阻抗分析仪对体系物相结构和介电性能进行了测试分析。结果表明：由于La,Ca和Mn,Ti的共存以及保持电中性的要求,该体系极易受从Mn^4 转变为Mn^3 的作用,在Mn含量不同时引入不同的空位缺陷,当Mn^3 含量与La^3 含量相当时体系中产生的缺陷相对最少,其介电常数最大,反之随两者含量偏差的增大而下降;La0.5Ca0.5MnxTi1-xO3分别在400～450℃和150～300℃之间出现2个介电峰。体系中La^3 和氧空位等产生的p型载流子和Mn离子变价引入的n型载流子在外电场下发生局域重排,产生了载流子极化,并在150～300℃范围被活化。同时由于这两种载流子对温度影响的响应不同,产生了与Mn离子的掺入相关的介电峰。在400～450℃范围,体系出现了相应为正交与立方结构转变的介电峰,也即Curie点。     

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.     

La2/3Sr1/3MnO3(La1.4Sr1.6Mn2O7)/Ce0.8Gd0.2O2-δ复合阴极的微观结构及热膨胀性能

采用固相反应法制备La2/3Sr1/3MnO3(LSMO3)粉体,用溶胶-凝胶法分别制备La1 4Sr1 6Mn2O7(LSMO7)和Ce0.8Gd0.2O2-δ(CGO)粉体.分别将LSMO3和LSMO7粉体与CGO粉体以1∶1的质量比均匀混合,在300MPa下冷等静压成型,并在1 500℃烧结2 h,制备了LSMO3/CGO和LSMO7/CGO复合阴极材料.研究了2种复合阴极材料的微观结构和热膨胀性能.结果表明:LSMO3/CGO与LSMO7/CGO烧结体在150～1 000℃温度范围内的平均线性热膨胀系数分别为1.52×10-5/K和1.53×10-5/K,与CGO固体电解质具有相近的热膨胀性能.烧结体断面形貌分析表明:LSMO3/CGO复合阴极具有与CGO相似的断面显微结构.     

Structural characterization and magnetic properties of single-crystalline (La0.6Pr0.4)0.67Ca0.33MnO3 nanowires

Herein, structural and magnetic properties of single-crystalline (La_0.6Pr_0.4)_0.67Ca_0.33MnO₃ nanowires synthesized via a hydrothermal process are reported. The nanowires are crystallized in an orthorhombic structure (Pnma space group). Their lattice parameters follow the relationship a ≈ c ≈ b/√2 These nanowires exhibited a clean and smooth surface with diameters of 60-120 nm and an average length of approximately 2.0 μm. High-resolution transmission electron microscopy images confirmed the single-crystalline nature of the nanowires growing along the [100] direction. The nanowires demonstrated magnetic hysteresis loops at low temperatures and a weak exchange bias (EB) effect. Paramagnetic (PM)–ferromagnetic (FM) phase transition occurred at a Curie temperature (T_C) of 224 K, and strong irreversibility between zero-field-cooled (ZFC) and field-cooled (FC) magnetization (M_ZFC and M_FC, respectively) curves was observed at 273 K. The M_ZFC curve exhibited a significantly broad peak with a maximum at a freezing temperature (T_f) of 134 K. Relative difference between M_FC and M_ZFC in the nanowires [(M_FC − M_ZFC)/M_FC] rapidly increased below T_f and reached approximately 50% below 35 K. The effective magnetic moment deduced from the Curie constant is larger than the theoretical value, indicating short-range FM interactions in the nanowires. A positive PM T_C (θ_p) implies dominant FM interactions in the nanowires, and θ_p > T_C observed herein indicates the existence of short-range ordered states above T_C.     

Robust temperature coefficient of resistance of polycrystalline La0.6Ca0.4MnO3 under magnetic fields at room temperature

In the presence of magnetic field, reducing the loss in temperature coefficient of resistance (TCR) and increasing metal−insulator transition point (T_MI) to room temperature are the most important concerns for the application of perovskite manganites in high−precision thermistors. Based on emerging evidence, relevant factor to address these problems lies in the interaction between Jahn−Teller (JT) distortion and magnetic field, which results in spin−orbital coupling (SOC) effect and significantly influences TCR and T_MI. In this work, we studied the magnetic field induced SOC effect in polycrystalline La_1−xCa_xMnO₃ (x = 0.225–0.45) materials synthesized via sol−gel technique. Compounds undergo the JT distortions with increasing Ca dopant content, and the most pronounced distortion of 0.0144 at x = 0.40 is correlated with a basal−plane distortion mode. All samples exhibit T_MI values between 262 K and 288 K, indicating the enhancement of doping−induced double−exchange interaction. In the magnetic field of 1 T, SOC effect sufficiently suppresses the deterioration of TCR caused by deficient magnetization in La_0.6Ca_0.4MnO₃ to a value of 2.9%·K⁻¹ at room temperature (287 K).     

Enhanced Microwave Absorption Properties of Intrinsically Core/shell Structured La0.6Sr0.4MnO3 Nanoparticles

The intrinsically core/shell structured La_0.6Sr_0.4MnO₃nanoparticles with amorphous shells and ferromagnetic cores have been prepared. The magnetic, dielectric and microwave absorption properties are investigated in the frequency range from 1 to 12 GHz. An optimal reflection loss of −41.1 dB is reached at 8.2 GHz with a matching thickness of 2.2 mm, the bandwidth with a reflection loss less than −10 dB is obtained in the 5.5–11.3 GHz range for absorber thicknesses of 1.5–2.5 mm. The excellent microwave absorption properties are a consequence of the better electromagnetic matching due to the existence of the protective amorphous shells, the ferromagnetic cores, as well as the particular core/shell microstructure. As a result, the La_0.6Sr_0.4MnO₃nanoparticles with amorphous shells and ferromagnetic cores may become attractive candidates for the new types of electromagnetic wave absorption materials.     

微量Ag掺杂对La_(0.6)Sr_(0.15)Na_(0.1)□_(0.15)MnO_3材料性质的影响

本文选用了La_(0.6)Sr_(0.15)Na_(0.1)□_(0.15)MnO_3(□为空位)为母体,用溶胶-凝胶方法制备了多晶样品Ag_(x-δ~-)La_(0.6)Sr_(0.15)Na_(0.1)Ag_δ□_(0.15-δ)MnO_3(x=0.00,0.016,0.04,0.1)。当x≥0.04时,其X光衍射谱上观察到了面心立方结构金属Ag相;掺杂样品的居里温度比未掺杂样品的要高,而且,随掺杂比例的增大而降低;掺杂样品在未加外磁场时的电阻率比未掺杂的要高,并随掺杂比例的增大而增大;当x=0.04时,MR在一个相当宽的温区内(207～286K)基本保持不变,即MR=(5.08±0.20)%,在一定程度上改善了母体样品MR的温度稳定性。     

EDTA-柠檬酸复合络合法制备阴极材料La_(0.4)Sr_(0.6)Co_(0.4)Fe_(0.6)O_3粉体

本文采用EDTA-柠檬酸复合络合法制备了SOFC阴极La_(0.4)Sr_(0.6)Co_(0.4)Fe_(0.6)O_3纳米粉体。并分别通过SEM、TEM、XRD及电化学极化阻抗仪对La_(0.4)Sr_(0.6)Co_(0.4)Fe_(0.6)O_3粉体形貌、尺寸、晶相及电化学性能进行了表征。实验结果表明:采用EDTA-柠檬酸复合络合法获得的干凝胶,经800℃煅烧后可获得粒径为20~30 nm、结晶度高的钙钛矿结构的La_(0.4)Sr_(0.6)Co_(0.4)Fe_(0.6)O_3纳米粉体。以La_(0.4)Sr_(0.6)Co_(0.4)Fe_(0.6)O_3粉体及添加20wt%的GDC粉体制备成的复合阴极在700℃下的极化阻抗为0.15Ω·cm~2、电导率为715 S·cm~(-1)。     

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.     

Synthesis of carbon nanotubes on La0.6Sr0.4CoO3 as substrate

A carbon nanotube/perovskite composite material was developed as material for air electrodes in fuel cells or zinc-air batteries. For this purpose, carbon nanotubes were directly grown on the perovskite La_0.6Sr_0.4CoO₃ impregnated with Fe solution which acted as substrate. The synthesis was carried out in a fluidised bed reactor. The carbon source was acetylene. The influence of the temperature on the growth of carbon nanotubes and on the stability of the perovskite was investigated. All samples contained multi-wall carbon nanotubes; however, at a temperature above 675 °C the perovskite was reduced by hydrogen originating from acetylene. The samples with the intact perovskite were further processed to air electrodes to catalyze the oxygen reduction reaction. These electrodes showed an improved performance compared to electrodes made of acetylene black and perovskites.     

Enhanced Thermoelectric Performance Induced by Cr Doping at Ca‐Sites in Ca3Co4O9 System

Thermoelectric performance of Ca₃Co₄O₉ system has been enhanced through the misplaced substitution with Cr doping at Ca‐sites. The study of Cr doping at Co‐sites has also been performed for comparing. Base on the analysis of the structural data, we conclude that the doped Cr ions should be in the form of Cr⁺⁶, and enter into Ca‐sites of Ca₂CoO₃ layers in Ca_3?xCr_xCo₄O₉ lattice and Co‐sites of CoO₂ layers in Ca₃Co_3.90Cr_0.10O₉ lattice, respectively. As Cr ions are doped into Ca‐sites in Ca_3?xCr_xCo₄O₉ lattice, both resistivity and thermopower increase obviously, while thermal conductivity decreases. Among all samples, Ca_2.95Cr_0.05Co₄O₉ shows the maximum ZT value, which is enhanced by 12% than that of Ca₃Co₄O₉. The results show that the misplaced substitution with a proper Cr doping at Ca‐sites is beneficial to the enhancement of the thermoelectric performance in Ca₃Co₄O₉ system compared to the traditional idea: Cr doping at Co‐sites, which is suggested to originate from the combined action of the carrier concentration, the electronic correlation, and the lattice disharmony.     

Electrochemical investigation of La0.4Sr0.6TiO3 synthesized in air for SOFC application

Journal of Applied Electrochemistry - La-doped titanate materials have been widely investigated as alternative Ni-free anodes for solid oxide fuel cells (SOFCs). In this study, La0.4Sr0.6TiO3 (LST)...     

多晶La0.67Ca0.33MnO3材料的热敏和湿敏特性

通过电阻温度测试系统来测试由La0.67Ca0.33MnO3多晶材料制成的敏感电阻,发现La0.67Ca0.33MnO3敏感电阻的电阻值不仅随着温度呈线性变化,而且也随着湿度呈线性变化。将封装后的La0.67Ca0.33MnO3敏感电阻与标准Pt100热敏电阻进行测温比较,相对误差为0.2%。