The Anomalous Optical Conductivity of Metallic La2?xSrxCuO4

The in-plane optical conductivity of three metallic La_2–x Sr _x CuO₄ single crystals with 0.10 x 0.15 has been studied between 30 and 295 K. Strong peaks in the far-infrared are observed, which cannot be explained by Drude-like models. Their similarity with peaks reported in Cu–O ladders with one-dimensional charge-ordering, their extremely low frequency, and their behavior with temperature allows us to conclude that those anomalous features are excitations of charge stripes in the Cu–O planes.     

La1-xSrxMnO3薄膜的制备、结构及电磁特性

以无机盐为原料,采用溶胶-凝胶工艺在Si衬底上制备La1-xSrxMnO3(LSMO)薄膜,XRD和TEM分析表明LSMO薄膜呈现纳米晶菱形钙钛矿结构,SEM分析表明LSMO薄膜表面平整、光滑致密。磁学测试结果表明:在0T、0.4T和0.8T时薄膜的Tp分别为220K、224K和229K,随着磁场的增大Tp移向高温的同时峰值电阻降低,这与铁磁相变及磁场对DE作用的影响有关。MR极值在250K左右达18.4%。     

涂料型La1-xSrxMnO3智能热控涂层的研究

以固相反应法制备了高纯度La0.8Sr0.2MnO3粉体,并以其为基料,磷酸二氢铝为粘结剂,采用涂覆工艺在铝基片上制备了涂料型La0.8Sr0.2MnO3热控涂层.采用XRD、EDS对La0.8Sr0.2MnO3粉体的成分进行了表征,用稳态卡计法测量了涂层在100~100℃温度区间内热辐射率随温度的变化,并测量了涂层的太阳吸收比.研究结果表明:粉体合成过程中,经过1200℃三次热处理制备的La0.8Sr0.2MnO3粉体纯度高,合成的粉体具有均匀的微米级粒径尺寸.通过适当调整浆料中La0.8Sr0.2MnO3粉体所占质量百分比,获得辐射率变化范围大于0.3的热控涂层,该性能与采用烧结工艺制备的La0.8Sr0.2MnO3陶瓷片材料在变温条件下的辐射率变化范围接近.该涂层在航天器热控技术中具有潜在的应用前景.     

Raman scattering investigation of the superconducting gap anisotropy in La2?xSrxCuO4

The low energy electronic Raman continua of a La_1.83Sr_0.17CuO₄ single crystal have been obtained in several different scattering geometries, and for temperatures above and below Tc. Based upon the polarization dependence of the spectra obtained for T Tc it is concluded that the superconducting gap is anisotropic with nodes located near the (±1,±1) directions in reciprocal space and maxima close to the kx and ky axes. The results are compared to spectra obtained from other high-Tc compounds and the possible compatibility of the results with particular gap functions is discussed.     

Griffiths Phase and Disorder in Perovskite Manganite Oxides La1?xCaxMnO3 and La0.7Sr0.3MnO3

Polycrystalline samples La_1−x Ca _x MnO₃ (x=0.17, 0.15, 0.10) and La_0.7Sr_0.3MnO₃ were prepared in order to investigate the Griffiths-like features induced by disorder compared with their counterpart single crystals. The magnetization data exhibit the traditional transition from ferromagnetic phase to paramagnetic phase. From the temperature dependence of inverse susceptibility, it can be testified that the Griffiths-like features still exist in as-prepared Ca doped samples, while non-Griffiths-like features exist in La_0.7Sr_0.3MnO₃. All these samples, however, exhibit the large effective spins resulting from formation of the short-order ferromagnetic clusters. The O K-edge X-ray absorption spectra indicate the Jahn–Teller (J-T) distortions are definitely present due to the J-T ion Mn³⁺, which indicate that static J-T distortion is not a sufficient condition for the existence of Griffiths phase in Sr-doped system. And, the size of J-T distortion is a little larger in polycrystalline La_0.7Sr_0.3MnO₃ than that in polycrystalline samples La_1−x Ca _x MnO₃ (x=0.17, 0.15, 0.10), revealed by X-ray diffraction parameters and extended X-ray fine structure absorption data of Mn K-edge. It also testifies that the disorder in La_0.7Sr_0.3MnO₃ caused by both chemical doping and J-T distortions is lower than that in polycrystalline samples La_1−x Ca _x MnO₃, which may be the reason of non-Griffiths-like phase existing in La_0.7Sr_0.3MnO₃ samples.     

The Optical Conductivity of La2?xSrxCuO4 in Connection with a Charge Stripe Scenario

The in-plane optical conductivity of La_2–xSr_xCuO₄ with 0.07 x 0.19 exhibits strong peaks in the far infrared. These features, which depend both on doping and temperature, can be associated with excitations of charge stripes, basing on results of different techniques on the same system and on recent theoretical calculations.     

Si衬底上La0.8Sr0.2MnO3/SrMnO3双层结构研究

利用磁控溅射方法在Si(100)衬底上首先生长SrMnO3(SMO)作为缓冲层,再沉积La0.8Sr0.2MnO3(LSMO)薄膜,得到(110)面择优生长的LSMO/SMO双层结构.利用X射线衍射仪分析了SMO缓冲层的结构特征对LSMO薄膜择优取向生长的影响;利用Rutherford背散射(RBS)分析了LSMO/SMO间的界面情况.结果表明以SMO作为单一缓冲层时,不仅可以实现LSMO薄膜在Si(100)衬底上的(110)面的择优生长,而且LSMO/SMO的界面扩散现象也不明显.     

La2/3Ca1/3MnO3∶Agx多晶靶材的制备及其电输运性质

采用固相反应法制备了不同Ag掺杂量的La2/3Ca1/3MnO3(LCMO)∶Agx(x为摩尔百分比,x=0.00、0.01、0.05、0.10、0.20、0.30、0.40)多晶靶材,XRD图谱显示所制备样品均为纯相的赝立方钙钛矿结构,并且随着Ag掺杂量的增加,a轴和b轴在0≤x≤0.40范围内有微小的涨落;另外R-T曲线显示,0≤x≤0.05时,金属-绝缘转变温度(Tp)开始升高很快,0.05相似文献   

La0.7Ca0.3MnO3薄膜微观结构的HRTEM表征

利用透射电子显微镜研究了衬底温度600～800℃条件下采用脉冲激光法在(001)LaAlO3(LAO)衬底上制备的La0.7Ca0.3MnO3(LCMO)薄膜的微观结构。结果表明薄膜由大量柱状晶组成且与LAO衬底形成良好外延关系。LCMO薄膜与LAO衬底的取向关系可以描述为:(ⅰ)(100)f∥(001)s、[011]f∥[100]s;(ⅱ)(011)f∥(001)s、[100]f∥[100]s。LCMO显示层状畴结构,即在衬底上初始生长的薄膜为(ⅱ)型畴,在此之上生长的薄膜为(ⅰ)类和(ⅱ)类型畴的混合体。薄膜中可观察到一些反向畴与孪晶等缺陷。薄膜与衬底界面少见错配位错,薄膜以Stranski-Krastanov模式生长。     

Heat conduction in Ba1?xKxBiO3

We have investigated heat conduction of single crystal Ba_1–xK_xBiO₃ in the temperature range of 2–300 K and in a magnetic field of up to 6 Tesla. Temperature dependence of thermal conductivity(T) reveals the participation of both electrons and phonons with their relative contributions that depend critically on the potassium doping concentration. Crystals underdoped with potassium (samples with higherT _c) exhibit a strong suppression of and a glass-like temperature dependence. In contrast, those with a higher potassium content (lowerT _c) show an increase as temperature decreases with a peak near 23 K. Field dependence of(H) is also very sensitive to the level of potassium doping. Crystals exhibiting a large phonon contribution show an initial drop in(H) at low fields followed by a minimum and then a slow rise to saturation as the field increases. The initial drop is due to the additional phonon scattering by magnetic vortices as the sample enters a mixed state. The high field behavior of(H), arising from a continuous break-up of Cooper pairs, exhibits scaling which suggests the presence of an unconventional superconducting gap structure in this material.     

多铁性BaTiO3/La2/3Sr1/3MnO3复合薄膜的制备及其强磁电效应的研究

使用脉冲激光沉积技术,在(001)取向的LaAlO3(LAO)单晶基片上外延生长了BaTiO3/La2/3Sr1/3MnO3(BTO/LSMO)双层复合薄膜.电学和磁学性能的研究显示复合薄膜具有较低的相对介电常数(εr=263),优良的铁电和铁磁性能以及高于室温的铁磁居里温度(Tc=317 K).复合薄膜的磁电电压系数(αE)为176 mV/A,高于同类结构磁电系统一个数量级,相应的界面耦合系数k值为0.68,表明铁磁层和铁电层界面之间存在较大程度的耦合.     

Cr替代Mn对La0.4Ca0.6MnO3磁性质的影响

用固相反应法制备了La0.4Ca0.6Mn1-xCrxO3(x=0.00,0.02,0.04,0.06,0.08,0.10,0.15)多晶样品,通过X射线衍射(XRD)图谱、磁化强度-温度(M-T)曲线、电子自旋共振(ESR)谱线,研究了Cr替代Mn对La0.4Ca0.6MnO3磁性质的影响.实验结果表明:La0.4Ca0.6MnO3存在复杂的磁结构,在258 K出现电荷有序相,从175 K到50 K,产生强关联CO-AFM(电荷有序?反铁磁)相,温度降到41 K左右出现自旋玻璃态;当替代量x≥0.06时,电荷有序相被融化;当x≥0.10时,自旋玻璃态被融化.对实验结果进行了初步解释:电荷有序相被融化主要原因是Cr3+与Mn4+具有相同的电子结构,Cr3+替代Mn3+破坏了CE型反铁磁的自旋序,从而引起电荷序的坍塌,实验证明了电荷序CE型反铁磁体系中,电荷序和自旋序之间存在强耦合相互作用;自旋玻璃态的融化,是由于Cr替代Mn破坏了自旋玻璃态的生成条件,即反铁磁背景下有少量铁磁成分.     

调控La2/3Sr1/3MnO3基异质结中磁各向异性变化的进展(英文)

钙钛矿锰酸盐(La_2/3Sr_1/3MnO₃)基异质结由于存在强自旋轨道耦合作用、高温铁磁性、强金属导电性以及丰富的氧八面体变化等特点,近年来在氧化物自旋电子学、拓扑电子态以及磁存储功能材料等应用方面备受关注.本综述主要针对锰酸盐异质结中磁各向异性变化,及其在氧化物自旋电子学器件中可能的应用进行了及时系统的总结.首先,本文简要介绍了锰酸盐异质结中的热点研究内容以及本文的出发点;其次,介绍了利用应变和衬底取向对锰酸盐异质结磁各向异性的调控;再次,重点介绍了界面耦合效应、氧八面体旋转、对称性破缺等新型界面工程手段对磁各向异性的调控;最后,介绍了电场调控磁各向异性的可逆变化方法,并总结了一些新型调控磁各向异性的手段.本综述将有效推动锰氧化物中磁各向异性的进一步研究,并且为锰氧化物在高效磁存储器件中的应用指明方向.     

RF plasma synthesis of YBa2Cu3O7?x powders

Fine powders of YBa₂Cu₃O_7–x have been synthesized by injecting mixed nitrate solutions of yttrium, barium, and copper into an argon rf thermal plasma. In general, the as-produced powders were dark brown and nonconducting. To obtain superconductivity, the as-produced powders were annealed either in a flowing oxygen tube furnace (at 900C) or in a lowpressure oxygen rf plasma. X-ray powder diffraction, scanning electron microscopy, and centrifugal sedimentation were used for powder characterization. For resistance measurements, bulk samples were prepared by isostatic pressing and tube furnace sintering of the annealed powders. The superconducting transition temperature (at 50% drop of resistivity) was 86 K.     

La0.7Sr0.3MnO3/α-Fe2O3复合材料的制备及吸波性能研究

以高温煅烧法制备了复合材料La_0.7Sr_0.3MnO₃/α-Fe₂O₃,并研究了其结构、电磁参数和吸波性能,进一步初步探索了该粉体用于布料涂层的吸波效果。结果发现：La_0.7Sr_0.3MnO₃/α-Fe₂O₃与石蜡以质量比7∶3混合后的吸波性能显著,分别在厚度5.0和9.5 mm处能吸收99.9%以上的入射电磁波,吸波性能优异。此外,在1～18 GHz和1.0～10 mm范围内,样品La_0.7Sr_0.3MnO₃/α-Fe₂O₃的总有效吸收(≦-10 dB)带宽覆盖测试带宽的91.8%,实现了雷达多频段的有效吸收。复合材料良好的吸波性能得益于La_0.7Sr_0.3MnO₃和α-Fe₂     

Oxygen Loss of the Manganite Surface Layer in La1 ? δMnO3/Metal Interface. Transport, XPS, and Photoconductivity Measurements

We report electrical measurements, XPS measurements, and photoconductivity on La_{1 –} MnO₃/metal interfaces. A clear evidence of a photo-induced insulator–metal transition of a La_0.81MnO₃/Al/Al₂O₃/Nb tunnel junction and second peak on R–T dependence of LaMnO₃/metal junctions are reported. These effects are explained in terms of formation of the La_{1 –} MnO₃ oxygen depleted layer caused by the out-diffusion of oxygen in La_{1 –} MnO₃/metal interface.     

La0.7-xNdxBa0.3MnO3纳米颗粒的居里温度与磁热效应

用溶胶-凝胶法制备了La0.7-xNdxBa0.3MnO3(x=0,0.05,0.10,0.15,0.20,0.25)多晶纳米颗粒,用XRD分析其相结构并计算晶格常数,用VSM测量样品的磁性能并计算磁熵变和居里温度.结果表明,La-Ba-Mn-O系列中适当的Nd掺杂可调整材料的居里温度至室温附近并有效提高其磁熵变.文中对于Nd掺杂对居里温度和磁熵变影响的机理进行了定性的分析.     

Effect of A-site vacancies on the magnetoresistive Effect in La1 ? x ? yCaxNayMnO3 ± δ

We have studied the effect of composition and heat-treatment conditions on the structural and transport properties of La_{1 − x − y} Ca _x Na _y MnO_{3 ± δ} solid solutions. The materials obtained offer a magnetoresistance of about 48% in a magnetic field of 1.2 MA/m.     

La1-xSrxMnAl11O19-δ催化剂的甲烷燃烧性能研究

采用反相微乳液-共沉淀法制备了一系列以La、Sr作为镜面阳离子、锰离子作为活性组分的六铝酸盐催化剂La1-xSrxMnAl11O19-δ(x=0.2、0.4、0.5、0.6、0.8)。利用X射线衍射、比表面积分析等分析方法及甲烷燃烧对催化剂的结构和性质进行了考察,主要考察了不同含量的La和Sr离子的掺杂量对催化剂结构及对甲烷催化燃烧活性的影响。结果表明,La和Sr同时作为镜面阳离子,不但可以形成完整的六铝酸盐,而且所制备的催化剂具有较高的催化活性。不同含量的La和Sr离子掺杂对于催化剂的特性有较大影响。当x=0.5时,所制备的催化剂La0.5-Sr0.5MnAl11O19-δ具有较高的催化活性,起燃温度T10%=502℃,至683℃甲烷完全转化。催化剂在低转化率下的宏观动力学实验结果表明,甲烷催化燃烧在La1-xSrxMnAl11O19-δ催化剂上为一级动力学反应,反应速率受催化剂固有性质控制。     

基于交替浸渍法对La0.65Sr0.35MnO3氧电极的性能优化

氢能以其高效、清洁、可再生的优点成为化石能源的有效替代者,而可逆固体氧化物电池(RSOC)既可利用氢气输出电能,也可电解H₂O产生氢气,对其研究具有十分重要的意义。本文对RSOC的氧电极进行了研究,在La_0.65Sr_0.35MnO₃(LSM)氧电极的基础上,采用溶液交替浸渍法将Sm_0.2Ce_0.8O_1.9(SDC)和Sm_0.5Sr_0.5CoO_3-δ(SSC)纳米粒子引入LSM氧电极中。800℃时,交替浸渍1次的LSM-SDC-SSC1氧电极的极化电阻为0.49Ω·cm²,是纯LSM电极(1.12Ω·cm²)的43%。SDC和SSC的浸渍顺序对电极形貌和性能的影响随着浸渍次数的增加逐渐减弱,交替浸渍2次的LSM-SDC-SSC2氧电极具有最低的极化过电位和极化电阻。800℃时,Ni-(Y₂O₃