Gd掺杂对La0.67 Sr0.33 CoO3、La0.67 Sr0.33 MnO3体系磁行为的影响

M~T curves and M~H curves of the systems La0.67Sr0.33CoO3, La0.67Sr0.33MnO3 (x=0.00, 0.05, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.67) were studied by experiments. Experimental results show that the magnetic structure of La0.67-xGdxSr0.33CoO3 system exhibits the cluster glass state with doping Gd increasing. The M~T curves of samples x>0.10 exhibit a peculiar phenomenon that M value rises sharply at low temperature range. The magnetic structure of La0.67-xGdxSr0.33MnO3 system changes from the long rang ferromagnetic order to the cluster glass state, and anti ferromagnetic state. The M~T curves of samples x≥0.50 decline sharply at low temperature range. The different phenomena shown by the two systems come from different coupling function between Gd and Co, Mn and from spin state transition of Co.     

静电纺丝法制备La0.67Ba0.33MnO3微纳米纤维及其红外发射率研究

采用静电纺丝法结合溶胶-凝胶技术制备了钙钛矿型La_0.67Ba_0.33MnO₃微纳米纤维, 并利用差示扫描量热-热失重分析(DSC-TGA)、 X射线衍射(XRD)、 傅里叶变换红外光谱(FTIR)和扫描电子显微镜(SEM)等技术对产物进行了表征, 利用IR-2红外发射率测试仪测试了La_0.67Ba_0.33MnO₃在280~370 K范围内的红外发射率. 结果表明, La_0.67Ba_0.33MnO₃在600 ℃时已形成钙钛矿结构. 随着煅烧温度的升高, La_0.67Ba_0.33MnO₃的形貌由纤维状向三维网络状转变, 并最终失去纤维形态. 在280~370 K范围内, La_0.67Ba_0.33MnO₃微纳米纤维的红外发射率随温度升高而升高, 由0.564增加至0.689. 利用钙钛矿材料双交换理论解释了这一现象, 并进一步探讨了其在红外发射率可变材料中的应用前景.     

La0.67Ba0.33MnO3中Bi掺杂产生的低场磁电阻增强效应

将Bi2O3掺杂到溶胶-凝胶法制备的La0.67Ba0.33MnO3(LBMO)微粉中, 结果发现随着Bi的掺杂, 材料的磁化强度和居里温度基本不变, 但电阻率发生明显变化, 在0～10% (摩尔分数)的掺杂范围内, 电阻率先急速上升后缓慢降低. 掺Bi可以使低温下的低场磁电阻得到显著增强, 但并不改变与双交换作用有关的本征磁电阻; 掺Bi也使室温下的磁电阻得到明显增强.     

Magnetic Susceptibility of Dilute La0.67Sr0.33MnO3-LaAlO3 Solid Solutions

Russian Journal of General Chemistry -     

Chemical and physical properties of complex perovskites in the La0.8Sr0.2MnO3−δ–La0.8Sr0.2CuO2.4+δ–La0.8Sr0.2FeO3−δ system

Perovskites resulting from discrete changes in composition within the quasi-ternary system La_0.8Sr_0.2MnO_3−δ–La_0.8Sr_0.2CuO_2.4+δ–La_0.8Sr_0.2FeO_3−δ were investigated under constant experimental conditions with the objective of obtaining an overview of the variation of the properties relevant for possible future applications. Nineteen nominal perovskite compositions within this system were systematically selected and synthesized under identical conditions by the Pechini method. The experimental data obtained on quantitative chemical analysis, powder X-ray diffraction, electrical conductivity and thermal expansion are presented collectively for the first time to facilitate comparisons. The formation and distribution of the different crystallographic phases at 950 °C within this quasi-ternary system are shown. The DC electrical conductivity is strongly influenced by the Cu content and increases up to 276 S cm⁻¹ for La_0.8Sr_0.2CuO_2.4+δ. The thermal expansion is dominated by the Cu/Mn ratio and is almost independent of the Fe content.     

La0.8Sr0.2MnO3／YSZ高温电极交流阻抗研究

用交流阻抗方法研究了Ｌａ０．８Ｓｒ０．２ＭｎＯ３电极上进行的氧化电化学还原反应。实验表明反应速度控制步骤随反应温度，氧分压及过电位发生显著变化，近平衡下反应的ｒｄｓ为氧的解离吸附过程。强阳极极化下，电解质表面产生大量电子空穴；强阴极极化下，ＬＳＭ电极表面形成大量氧空位，二者的结果均使界面电导增加，电化学反应区扩展。     

Enhanced magnetoresistance in La0.7Sr0.3MnO3 nanoscaled granular composites

By soft chemical processing, two kinds of nanoscaled lanthanum manganite granular composites, La0.7Sr0.3MnO3/CoFe2O4 (LSMO/CF) and La0.7Sr0.3MnO3 / Nd0.7Sr0.3MnO3 (LSMO/ NSMO), were fabricated. Enhancement in magnetoresistance is observed in both of the composites. Different magnetic compounds, CF and NSMO, embedded in LSMO matrix, result in different temperature ranges where the enhancement occurs. It is considered that the phenomenon is associated with electron tunneling between sorts of grains as well as spin-dependent scattering.     

高温合成锰酸锶镧的缺陷

严格按照化学式拟定配方,采用固相合成方法合成的锰酸锶镧材料中含有杂相La2O3.借助XRD,DSC,TG等分析手段分析了高温合成锰酸锶镧的缺陷,尝试对锰酸锶镧进行高温再处理,结果获得的纯锰酸锶镧不含La2O3杂相.     

La0.8Sr0.2MnO3水基料浆稳定性的研究

通过调节pH值和添加分散剂的量来研究La0.8Sr0.2MnO3水基料浆的悬浮性和稳定性.结果表明, pH在碱性条件下(pH>8),分散剂添加量为0.2% 时,锰酸镧水基料浆具有良好的稳定性.     

Effect of TiO2 nanorod thickness on optical properties of Ba0.8Sr0.2TiO3 film via hydrothermal method

Journal of Solid State Electrochemistry - Hydrothermally produced perovskite-type barium strontium titanate Ba0.8Sr0.2TiO3 (BST) nanorods deposited on TiO2 substrate for 2 h at...     

The layer‐by‐layer stoichiometry of La0.7Sr0.3MnO3/SrTiO3 thin films and interfaces

By using a combination of synchrotron photoemission and a finite element model, the layer‐by‐layer stoichiometry of pulsed laser deposited La_0.7Sr_0.3MnO₃ (LSMO) thin films is extracted. For 3‐ and 5‐unit‐cell films, the LSMO stoichiometry at the LSMO/SrTiO₃ interface has been studied, and it is found that the Sr surface segregation is reversed at the lower interface such that it becomes La rich and Sr depleted. Mn is depleted throughout the entire layer, consistent with reports of a magnetically ‘dead’ layer and the formation of a Ruddlesden–Popper phase. The depth‐averaged Mn concentration is less than 50% of the expected value, suggesting that interface mixing or segregation into the bulk is important, whereas the depth‐averaged La and Sr concentrations are close to the expected values. Copyright © 2013 John Wiley & Sons, Ltd.     

La0.8Sr0.2Ga0.8Mg0.2O3与La0.8Sr0.2Ga0.8Mg0.15Co0.05O3电导的对比

采用固相合成法制备了La0.8Sr0.2Ga0.8Mg0.2O3(LSGM8282)和La0.8Sr0.2Ga0.8Mg0.15Co0.05O3 (LSGMC5), 利用四电极交流阻抗法和Hebb-Wagner 极化法对比研究了两种材料的总电导率和电子电导率. 实验结果表明, LSGM8282 的总电导率与氧分压无明显依赖关系, 而LSGMC5 的总电导率在高氧分压区随氧分压降低而增加,在中等氧分压区域基本保持不变. 在973-1173 K的温度范围内, LSGM8282的自由电子电导率以及电子空穴电导率的氧分压级数分别为-1/4和1/4.在1073-1173 K的温度范围内, LSGMC5的自由电子电导率以及电子空穴电导率的氧分压级数分别为-1/4和约为1/8, 表明LSGMC5的空穴产生机制可能与LSGM8282不同. LSGM8282 的氧离子电导率与氧分压无关, 而LSGMC5 的氧离子电导率在高氧分压区随氧分压的减小而增加.     

Single crystalline La0.7Sr0.3MnO3 molecular sieve nanowires with high temperature ferromagnetism

Porous mixed-valent manganese oxides are a group of multifunctional materials that can be used as molecular sieves, catalysts, battery materials, and gas sensors. However, material properties and thus activity can vary significantly with different synthesis methods or process conditions, such as temperature and time. Here, we report on a new synthesis route for MnO(2) and LaSr-doped molecular sieve single crystalline nanowires based on a solution chemistry methodology combined with the use of nanoporous polymer templates supported on top of single crystalline substrates. Because of the confined nucleation in high aspect ratio nanopores and of the high temperatures attained, new structures with novel physical properties have been produced. During the calcination process, the nucleation and crystallization of ε-MnO(2) nanoparticles with a new hexagonal structure is promoted. These nanoparticles generated up to 30 μm long and flexible hexagonal nanowires at mild growth temperatures (T(g) = 700 °C) as a consequence of the large crystallographic anisotropy of ε-MnO(2). The nanocrystallites of MnO(2) formed at low temperatures serve as seeds for the growth of La(0.7)Sr(0.3)MnO(3) nanowires at growth temperatures above 800 °C, through the diffusion of La and Sr into the empty 1D-channels of ε-MnO(2). Our particular growth method has allowed the synthesis of single crystalline molecular sieve (LaSr-2 × 4) monoclinic nanowires with composition La(0.7)Sr(0.3)MnO(3) and with ordered arrangement of La(3+) and Sr(2+) cations inside the 1D-channels. These nanowires exhibit ferromagnetic ordering with strongly enhanced Curie temperature (T(c) > 500 K) that probably results from the new crystallographic order and from the mixed valence of manganese.     

Microstructure,magnetoelectric properties and leakage mechanisms of La0.7Ca0.3MnO3/Bi3.15Nd0.85TiO3 composite thin films

A series of high quality Bi_3.15Nd_0.85TiO₃ (BNT) ferroelectric thin films and La_0.7Ca_0.3MnO₃/Bi_3.15Nd_0.85TiO₃ (LCMO/BNT) multiferroic composite thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by chemical solution deposition (CSD) method. The microstructure, surface morphology and leakage mechanisms of BNT and LCMO/BNT composite films were revealed by X-ray diffraction, scanning electron microscopy and semiconductor device analyzer, respectively. Ferroelectric behavior along with a remnant polarization (2P_r) of 20 μC/cm², saturated magnetization around 56 emu/cm³ and magnetoelectric effect (ME) voltage coefficient α_ME of 33 mV/cm Oe at 1 kHz for LCMO/BNT composite films were obtained at room temperature, indicating that the coupling effects of electric and magnetic field exist in the fabricated LCMO/BNT multiferroic composite thin films. And our observations provide an effective way to manipulate the conduction behavior and push forward understanding the leakage mechanism in LCMO/BNT composite films.     

Synthesis,structural, magnetic and magnetocaloric properties of La0.8Sr0.2MnO3 nanoparticles

In this work, we reported a detailed study on the synthesis, structural and magnetic properties of nanocrystalline La_0.8Sr_0.2MnO₃. The synthesized nanoparticles were prepared using a sol–gel method and characterized using X-ray diffraction and high-resolution transmission electron microscope. The average particle size was found in the range from 40 to 45 nm. The magnetization versus temperature M(T) measurements as well as magnetization field dependence M(H) have been investigated using vibrating-sample magnetometer. The magnetization as a function of temperature M(T) indicated a broad second-order magnetic phase transition from ferromagnetic state to paramagnetic state in the Curie temperature region (320–340 K). The magnetocaloric effect of the sample has been estimated and presented a maximum magnetic entropy change |ΔS_M|_max?=?0.86 J kg^?1 K^?1 with relative cooling power?=?62.12 J kg^?1 at magnetic field (H)?=?2T. Based on the result of magnetocaloric properties, the investigated sample could be considered as a good refrigerant material for near room temperature magnetic refrigeration.

     

微观结构对溶胶-凝胶法合成的La0.67Sr0.33MnO3电磁性能影响

采用溶胶-凝胶法制备了不同烧结温度的钙钛矿类锰氧化物La0.67Sr0.33MnO3样品。实验结果表明,在1573 K以上烧结的样品,晶粒出现异常长大,晶界效应明显。随着烧结温度的提高,磁化强度逐渐增大,但样品的居里温度基本不变。此外,在1173和1573 K温度下烧结的样品,均出现了低于居里温度的金属-半导体导电行为转变。在合适的烧结条件下,可以观察到隧道磁电阻(TMR)和超大磁电阻(CMR)2种磁电阻效应。实验表明,自旋电子的输运,不仅与样品平均粒径的大小和密度有关,而且与晶界的微观结构有密切关系。