钙钛矿材料La0.65Ca0.35Mn1-xFexO3的低场磁电阻特性探讨

我们制备了氧化物材料科La0.65Ca0.35Mn1-xFexO3(x=0,0.01,0.02,0.03),研究了材料在低场0.57T下的磁电阻效应,我们发现氧化物材料La0.65Ca0.35Mn1-xFexO3据里温度Tc及电阻峰位温度Tp均值铁含量的增加而下降,这主要是因为Fe离子不参加双交换作用,且阻挡了双交换作用的进行,材料的铁磁作用随铁含量增加而减弱。利用迪尼模型计算了La0.65Ca0.35Mn1-xFexO3材料在零场及磁场为0.57T下电阻随温度的变化关系,理论计算结果与实验数据吻合得较好。     

掺Ag磁性氧化物的庞磁电阻效应

本文重点介绍了掺Ag的钙钛矿锰氧化物和磁铁矿的磁电阻增强效应。结构分析表明，这些材料是由铁磁性的钙钛矿锰氧化物相或亚铁磁性的磁铁矿相与非磁性的金属Ag相所组成的两相复合物。由于金属Ag相的存在，它们的低场磁电阻效应明显增强。这可归因于传导电子在磁性相和非磁性相界面处的自旋相关散射的增强。     

(La2/3Ca1/3)(Mn(3-x)/3)Fex/3)O3体系磁电阻行为的研究

通过系统地测量（La2/3Ca1/3）（Mn（3-x）／3Fex／3）O3（x＝0、0.1、0．2、0．3的体系样品的电阻率-温度关系以及一定温度下磁电阻率与磁场的关系,发现随x的变化其磁电阻率峰和电阻率峰均发生位移,磁电阻率峰值增大,并伴生磁电阻率峰展宽效应．作者认为由于Fe的替代,引起体系中Mn3 ／Mn4 比率及磁矩的变化,加之外场对磁有序结构的调制作用,从而影响了Mn3 －O－Mn4 的双交换作用,最终导致磁电阻行为发生变化．     

微观缺陷和3d电子对La2/3Ca1/3Mn1-xFexO3陶瓷磁电阻性能的影响

用符合正电子湮没辐射Doppler展宽技术研究了La2/3Ca1/3Mn1-xFexO3陶瓷的缺陷和3d电子行为。结果表明:对x≤0.33的样品,随着样品中Fe含量的增加,3d电子数量增加,样品的商谱谱峰升高;对x>0.50的样品,随着样品中Fe含量的增加,样品中有新相生成,体系缺陷增加,样品的商谱谱峰降低。测试了La2/3Ca1/3Mn1-x-FexO3多晶陶瓷的磁电阻性能,讨论了微观缺陷和3d电子对La2/3Ca1/3Mn1-xFexO3多晶陶瓷磁电阻性能的影响。     

La1-xCaxMn1.03O3外延薄膜的巨磁电阻效应

研究了用溶胶－凝胶（ｓｏｌ－ｇｅｌ）方法在ＬａＡｌＯ３（１００）衬底上制备的Ｌａ－１ｘＣａｘＭｎ１．０３Ｏ３外延薄膜的磁电阻效应。ｘ在０．２～０．６２１范围内变化,外延薄膜的电阻率与温度的关系从类半导体行为向金属导电行为转变。在ｘ≥０．５的４个样品中没有发现电荷有序绝缘体（ＣＯＩ）和反铁磁绝缘体（ＡＦＩ）现象。ｘ＝０．２样品在１．５Ｔ磁场下磁电阻率ＭＲ的最大值为１０＾４％、磁转变温度为２３０Ｋ。     

大磁电阻材料La0.67Ca0.33Mn1-xNixO3的研究

我们制备了La0.67Ca0.33Mn1-xNixO3氧化物材料,测量了热磁曲线,其居里温度随镍含量增加而减少,这是由于Mn^3 /Mn^4 双交换作用随镍对锰的替代减弱的结果。测量了材料的大磁电阻效应,并利用迪尼模型计算分析了含镍材料在零场以及磁场为6T下电阻随温度的变化关系。实验与计算对照结果表明：迪尼模型可以很好地描述对应于铁磁／顺磁相变的电阻峰值现象。     

复合相结构钙钛矿锰氧化物低场磁电阻效应

阐述了低场磁电阻及其产生的物理机制,综述了国内外近年来在复合相钙钛矿锰氧化物低场磁电阻增强这一研究领域的进展及其存在的问题.在母相中添加第二相物质形成复合相结构是低场增强磁电阻最简单和有效的方法.结合实践需要和自身研究结果提出制备复合相钙钛矿锰氧化物的新方法,即粘接法,用此方法制备出的复相材料具有很好的应用潜力.     

Fe/Al2O3/Fe隧道结的巨磁电阻效应

研究了Fe(200℃退火)/Al2O3/Fe多层膜隧道结的巨磁电阻效应,在室温下获得了5.89％的巨磁电阻效应,并且测量了样品的伏安曲线,证明了隧道效应的存在。     

(La2/3Ca1/3)(Mn(3-x)/3Fex/3)O3体系磁电阻行为的研究

通过系统地测量(La     

La—Gd—Ca—Mn—O的磁性、电性和磁电阻效应

在La0.67C0.33MnO3中进行了掺Gd研究，结果发现，经1400℃烧结的样品，获得了最佳的磁电阻效应，随掺Gd量增加，材料的相变温度逐渐下降，对应的降值的电阻率大幅度增加，居里温度逐渐下降，磁电阻比明提高，掺入11％的Gd后，可以使磁电阻比提高一个数量极，这些变化可以用晶格效应来解释。     

Catalytic decomposition of NO over brownmillerite-like compounds,Ca2Fe2O5 and Sr2Fe2O5

A high-temperature form of a brownmillerite-like compound Sr₂Fe₂O₅, which has a perovskite structure with the oxygen vacancies randomly distributed, showed a remarkable NO decomposition at 700–900°C, whereas another brownmillerite-like ferrate (III) of composition Ca₂Fe₂O₅ did not exhibit any significant catalytic activity for NO decomposition over the temperature range from room temperature to 900°C. This difference in their catalytic activities has been explained on the basis of their crystallographic properties, i.e., ordering or disordering of the oxygen deficiencies.     

Synthesis, structure and magnetic properties of Sr2Fe1−xGaxMoO6 (0 ≤ x ≤ 0.6) double perovskites

Polycrystalline Sr₂Fe_1−xGa_xMoO₆ (0 ≤ x ≤ 0.6) materials have been synthesized by solid state reaction method and studied by neutron powder diffraction (NPD) and magnetization measurements. Rietveld analysis of the temperature dependent NPD data shows that the compounds crystallize in the tetragonal symmetry in the space group I4/m. The anti-site (AS) defects concentration increases with Ga doping, giving rise to highly B-site disordered materials. Ga doping at the Fe-site decreases the cell volume. The evolution of bond lengths and the cation oxidation states was determined from the Rietveld refinement data. The saturation magnetization and Curie temperature decreased with the increasing Ga content in the samples. Low temperature neutron diffraction data analysis and magnetization measurements confirm the magnetic interaction as ferrimagnetic in the sample.     

Er2-xRxFe17(R=Pr,Ce)化合物的结构与磁熵变研究

在氩保护气氛中用熔炼法制备了Er2-xRxFe17(R=Pr,Ce)系列合金,通过粉末X射线衍射和SQUID磁强计研究了样品的结构和磁熵变.结果表明,轻稀土Pr和Ce的掺入没有明显改变Er2Fe17化合物的相结构,但改变了Er次晶格与Fe次晶格之间的耦合系数,使仍为六方Th2Ni17型结构的Er2-xRxFe17化合物的居里温度可通过成分微调使其处在室温附近,Er2-xRxFe17化合物的λ形(-△SM)-T曲线表明其在居里点附近发生的相变属于二级相变,Er2-xRxFe17化合物有较大的磁熵变,且致冷温区较宽,是一类有很大应用潜力的室温磁致冷材料.     

Ionic conductivity and crystallographic data for Na2-xCa1-xAlxSiO4 and Na2-xCaSi1-xPxO4 carnegieite phases

Single crystals of Na₂CaSiO₄ prepared at 30 kbar and 1500°C are cubic with $\text{a}\text{= 22.456}\text{A}\text{?}$. The polycrystalline compositions Na_1.9Ca_0.9Al_0.1SiO₄ and Na_1.8CaSi_0.8P_0.2O₄ can also be indexed using $\text{a}\text{= 22.458}\text{and}\text{22.471}\text{A}\text{?}$, respectively. The Ca carnegieites Na₂CaSiO₄, Na_1.9Ca_0.9Al_0.1SiO₄, and Na_1.8CaSi_0.8P_0.2O₄ have Na ion conductivities of only 5?8 × 10^?6 (ω-cm)^?1 at 300°C.     

Ba2Fe1+xMo1-xO6双钙钛矿的制备与磁卡效应

采用湿化学法制备了一系列Ba2Fe1+xMo1-xO6双钙钛矿材料,研究了Fe/Mo原子比对其磁性能尤其是磁卡效应的影响.实验结果表明,随着x增加,样品的磁化强度由x=0时的37.3A·m2/kg(3.49μB/f.u.)下降到x=0.3时30.4A·m2/kg(2.78μB/f.u.);当x=0时,样品的最大磁熵变值为1.54J/kg·K.随着x增加,样品的最大磁熵变值逐渐下降,磁熵变随温度变化曲线的峰形变宽.     

The synthesis and selected properties of new compounds: Mg3Fe4(VO4)6 and Zn3Fe4(VO4)6

New compounds: Mg₃Fe₄(VO₄)₆ and Zn₃Fe₄(VO₄)₆ were obtained from a solid state reaction. The temperatures of melting of Mg₃Fe₄(VO₄)₆ and Zn₃Fe₄(VO₄)₆ amount to 950±5 and 850±5°C, respectively. The indexing results and the calculated unit cell parameters for both compounds are given and suggest that both phases are isotypic with Mn₃Fe₄(VO₄)₆. The IR spectra of the above-mentioned compounds are presented.     

Enhanced magnetic behavior of Al substituted LaFeO3 (La(1 − x)AlxFeO3, x = 0.10 and 0.30)

La_(1 − x)Al_xFeO₃ (x = 0, 0.1, 0.3) has been prepared by solid state reaction method. The formation of pure crystallographic phase of LaFeO₃ and the substitution of Al³⁺ in all the doped samples have been confirmed by Rietveld analysis. The magnetic measurements viz., magnetization curves, hysteresis loops etc. in the temperature range 300-5 K showed that magnetization of the doped samples has been appreciably enhanced compared to that of the pristine LaFeO₃. The maximum enhancement factor of ~ 19 for saturation magnetization measured at room temperature has been found in La_0.7Al_0.3FeO₃.     

Phase relationships in the system HxMoO3 (0<x⩽2.0)

Four solid phases of H_xMoO₃ in the range 0<x?2.0 have been synthesised and characterised following Glemser and co-workers (1, 2, 3). Unit-cell dimensions for all phases have been determined from Guinier powder X-ray analysis. Ranges of homogeneity exist for three of the phases and approximate limits have been determined as follows: blue orthorhombic 0.23<x<0.4, blue monoclinic 0.85<x<1.04, red monoclinic 1.55<x<1.72.     

K2(Rb2,Cs2,Tl2)TeBr6(I6) and Rb3(Cs3)Sb2(Bi2)Br9(I9) perovskite compounds

We systematize available experimental data on the crystal structure of the ternary halides K₂(Rb₂,Cs₂,Tl₂)TeBr₆(I₆) and Rb₃(Cs₃)Sb₂(Bi₂)Br₉(I₉), analyze the general trends in the properties of their single crystals, and examine the key features of the physicochemical interaction in related systems.