在氧-水蒸气存在下单相Sr2(Gd,Ce)2Cu2RuO10的合成及其电学性质

传统固相反应所合成的锶系钌铜氧化物，通常总伴有少量铁磁性SrRuO₃杂相.采 用氧(或空 气)_水蒸气混合气氛下的新型固相反应，既能成功合成锶系钌铜氧化物的前驱物纯相Sr₂G dRuO₆(211相), 也能进一步在相对低的温度下成功合成锶系钌铜氧1222纯相化 合物RuSr₂(Gd,Ce)₂Cu₂O₁₀ (Ru_1222）， 使其中SrRuO _{关键词： 水蒸气参与的新型固相反应 2}(Gd')" href="#">RuSr₂(Gd 2Cu_{2< /sub>O10纯相')" href="#">Ce)2Cu2< /sub>O10纯相 3杂相')" href="#">SrRuO3杂相 电学性质}     

高纯度超导氧化物RuSr2GdCu2O8的合成与超导电性

RuSr2GdCu2O8据报道是转变温度为30－40K的超导体，其合成的主要问题是，在合成过程中有相当多的铁磁性的SrRuO3杂相伴随着主相一起生成，本文报道了合成RuSr2GdCu2O8（Ru-1212相）纯相的新方法，即在O2和水蒸气气氛中首先合成纯相的Sr2GdRuO6(Ru-211相）先驱物，然后Sr2GcRuO6与CuO高温烧结，生成RuSr2GdCu2O8。合成的RuSr2GdCu2O8电阻为半导体温度行为，该体系的超导转变与生成的杂相有关。     

氧-水蒸汽中Sr2GdRuO6纯相的合成及固相反应机理

采用氧 (或空气 ) 水蒸汽混合气氛下的固相反应 ,可合成无任何SrRuO3 杂相的纯相化合物Sr2 GdRuO6.当由Sr2 GdRuO6作先驱物 ,类似的固相反应体系 ,可成功合成无任何SrRuO3 杂相的纯相RuSr2 GdCu2 O8化合物 .此外 ,还讨论了有水蒸汽参与的固相反应合成Sr2 GdRuO6的反应机理 .结果表明 ,水蒸气的作用是抑制SrRuO3 的形成 ,而不是有利于把SrRuO3 杂相转化为Sr2 GdRuO6相 .     

(Hg,M)-1222相铜氧化合物的合成及其超导电性研究(M=W、Mo、Ti、V、Cr)

分别用固相反应和柠檬酸盐溶胶－凝胶法制备义组成为Sr2(Gd1.5Ce0.5)Cu2Oz的前驱物,再用真空烧结的方法合成了（Hg,M)－1222相铜氧化合物（Hg0.75M0.25)Sr2(Gd1.5Ce0.5)Cu2Oz(M=W,Mo,V,Cr,Ti)。溶胶－凝胶法同固相法相比混合更均匀,反应温度低,成相情况好,改进该方法后,用溶解度较高的Ce（NO3）3代替不溶于硝酸的CeO2,制得了纯1222相。研究了不同退火条件对样品电阻温度特性的影响的影响,发现高氧压退火有助于超导转变,M＝W,Mo时得到超导体,Tc(onset)在13－27K之间。     

Ru1222体系的红外吸收光谱研究

我们详细研究了Ru1-xSbxSr2Gd1.4Ce0.6Cu2O10-δ(Ru1222Gd)和RuSr2Sm2-yCeyCu2O10-δ(Ru1222Sm)系列样品的红外吸收光谱.实验结果表明,样品在680 cm-1,600 cm-1,530 cm-1,400,380cm-1附近分别出现典型的红外吸收峰.通过与类似结构的高温超导体进行比较,对吸收峰进行了指认和分析.同时,我们还分析讨论了体系的晶格结构、声子振动和输运性质的相互关系.研究结果表明,Sb掺杂和Ce含量的变化对平面氧O(3)沿a轴的伸缩振动和顶点氧0(2)沿z轴的伸缩振动有着不同的影响.     

超导铁磁体RuSr2Gd1.4Ce0.6Cu2O10-δ的输运性质和磁共振研究

本文对RuSr2Gd1.4Ce0.6Cu2O10-δ样品的微结构、输运性质及磁共振性质进行了实验研究。研究表明RuSr2Gd1.4Ce0.6Cu2O10-δ样品的晶格参数自280K至30K缓慢下降。长时间流动氧气退火可提高零电阻转变温度（Tc(0)），但不影响超导起始转变温度（Tc(onset)）。正常态电阻在110K和180K附近有一微小波动，可能是由于RuO2面载流子与Ru磁矩之间交换作用引起的自旋散射降低所至。电子顺磁共振测量显示有两个只收峰，其中一个对应Gd离子的电子顺磁共振（EPR），另外一个在铁磁转变温度以下出现，它对应Ru离子的铁磁共振（FMR）。本文对磁共振谱的线宽、强度和g因子随温度的变化进行了探讨。     

烧绿石型富氧相Ce_2Zr_2O_8与缺氧相Nd_2Zr_2O_7的振动光谱及XPS对比研究

采用石墨还原法成功制备了富氧相Ce2Zr2O8,选用缺氧相Nd2Zr2O7替代其前驱体CeZrO3.5+δ进行结构对比分析,利用X射线衍射(XRD)、拉曼光谱(Raman)、红外光谱(IR)及X射线光电子能谱(XPS)对样品体、表晶体结构进行表征。XRD结果表明,Ce2Zr2O8相具有典型烧绿石结构特征,表征Ce/Zr阳离子有序排列的超结构峰非常明显,但其Zr—O配位体由前驱体中的[ZrO6]八面体转变为[ZrO8]立方体,[ZrO8]配位体形成大大降低了Ce2Zr2O8的结构稳定性。Raman和IR结果表明,Ce2Zr2O8相的振动光谱谱带比其前驱体替代物Nd2Zr2O7显著增多,说明氧离子的富集导致Ce2Zr2O8相中某些振动简并峰消除简并,该结果进一步证实了其结构对称性较前驱体更低。XPS结果表明,Ce2Zr2O8相表面Ce(Ⅳ)特征峰(916.3eV)非常明显,没有Ce(Ⅲ)特征峰(885eV)出现,说明该相前驱体中的Ce3+已被完全氧化成Ce4+;Ce2Zr2O8相中Zr(3d)结合能与萤石相Gd1.2U0.8Zr2O7+y接近证实其表面形成了与体相一致的[ZrO8]配体;O(1s)低位结合能升高表明Ce2Zr2O8体相氧种介于晶格氧和吸附氧之间,高位氧峰出现说明其表面含有吸附氧,吸附氧与Ce2Zr2O8体相结合强度介于CeO2和Nd2Zr2O7之间。     

KAlF_4∶Ce,Gd磷光体的荧光特性及能量传递

采用溶液反应和固相反应 ,分别合成了KAlF4 基质化合物及KAlF4 ∶Gd和KAlF4 ∶Ce ,Gd等磷光体 ,研究了它们的光谱特性。结果表明 ,KAlF4 ∶Gd无论在短波或长波紫外辐射激发下 ,均无任何吸收和发射。在KAlF4 ∶Ce,Gd中 ,Ce3 + 离子能有效地将能量传递给Gd3 + 离子 ,使Gd3 + 产生了特征锐发射 ,且发射强度很大。但当Ce3 + 浓度固定不变 ,改变Gd3 + 的浓度时 ,Gd3 + 的 6P1/ 2 → 8S7/ 2 发射强度随Gd3 + 浓度的增大反而减弱。     

La4(P2O7)3：Ce,Gd,Tb磷光体的合成与光谱性质

本文首次采用溶液沉淀法合成了一系列La4(P2O7)3;Ce,Gd,Tb磷光体.经X射线分析表明,它们属于纯的La4(P2O7)3相。测定了这些化合物的激发和发射光谱、相对亮度及Ce3+的发光寿命,观察到在此基质中Ce3+与Gd3+的光谱重叠,它们之间存在着一定的相互作用,使(La0.64Ce0.3Gd0.064(P2O7)3的亮度比(La0.7Ce0.34(P2O7)3和(La0.94Gd0.064(P2O7)3有少许增加.此外,Ce3+能有效地敏化Tb3+9,从而大大增强Tb3+的发射.然而,Gd3+与Tb3+共存时存在着竞争吸收和独自发射,使(La0.80Gd0.06Tb0.144(P2O7)3的亮度与单掺的(La0.86Tb0.144(P2O7)3相比有少许降低.相应地在Ce,Gd和Tb共掺时,由于Gd3+的影响,使Tb3+的发射减弱,从而总的发光相对亮度有所降低。     

(Ce,Gd,Mn)MgB5O10磷光体的合成及其发光

本文采用固相反应的方法合成了一系列(Ce,Gd,Mn)MgB5O10磷光体。观察到合成温度、灼烧时间、原料配比对磷光体的形成和发光亮度有重要影响。X射线衍射分析表明,磷光体结构与LaMgB5O10相同,属单斜晶系、空间群P21/c。用EPR确定了磷光体中锰离子为二价。测定了(Ce0.2La0.2)MgB5O10,(Gd0.7La0.3)MgB5O10,(Mn0.05La0.95)MgB5O10,(Ce0.2Mn0.05La0.75)MgB5O10,(Gd0.95Mn0.05)MgB5O10、(Ce0.2Gd0.8)MgB5O10和(Ce0.2Gd0.75Mn0.05)MgB5O15等磷光体的光谱。根据光谱数据讨论了(Ce0.2Gd0.75Mn0.05)MgB5O10磷光体中能量传递过程为:Ce3+→Mn2+,Gd3+→Mn2+以及Ce3+→Gd3+→Mn2+,其中Ce3+离子可将能量高效地传递给Gd3+,Gd3+离子起着中间体的作用。     

Magnetic ordering in HoRu2Si2, HoRh2Si2, TbRh2Si2 and TbIr2Si2 by neutron diffraction

Neutron diffraction study of polycrystalline HoRu₂Si₂, HoRh₂Si₂, TbRh₂Si₂, and TbIr₂Si₂ was performed in the temperature range between 4.2 and 300 K. For HoRu₂Si₂ the magnetic spin alignment of a linear transverse wave mode below the Néel temperature 19 K is observed. This static moment wave is propagating along the b-axis with k=(0, 0.2, 0) and is polarized in the c-axis. The root-mean-square and maximum saturation moments per Ho atom are 9.26 and 13.09μ_B, respectively. HoRh₂Si₂, TbRh₂Si₂ an TbIr₂Si₂ are simple collinear antiferromagnets of +-+- type with Néel temperatures of (27±1), (98±2) and (72±3) K, respectively. For TbRh₂Si₂ and TbIr₂Si₂ magnetic moments are localized on RE ions only and are aligned along the tetragonal axis, while for HoRh₂Si₂ they form an angle ø = (28±3)°.     

μ+SR study of LaNi2As2, URh2Si2 and CeRh2Si2

Muon spin relaxation experiments have been carried out in the paramagnetic and magnetically ordered states of URh₂Si₂ and CeRh₂Si₂. As the magnetic structure of these compounds is well known, these measurements can help to characterise their magnetic properties probed by μSR and to understand the μSR results of the heavy fermion compounds of the same crystallographic family. Our measurements show that the muons occupy two different crystallographic sites. The spectra of URh₂Si₂ and CeRh₂Si₂ in the magnetically ordered states are very different, probably reflecting their different magnetic structures. The spectra obtained on CeRh₂Si₂ are similar to the published spectra of the heavy fermion compound CeCu_2.1 Si₂. Muon spin rotation measurements on LaNi₂As₂ indicate that the muon is diffusing at 150 K.     

13C-selective IRMPD of CBr2F2/Cl2 and CCl2F2/Br2 systems

The CO₂ TEA laser irradiation of CBr₂F₂ in the presence of Cl₂ yielded ¹³C-enriched CBrClF₂ and ¹³C-enriched CCl₂F₂ under selected experimental conditions. As the photolysis proceeded, the ¹³C concentration of CBrClF₂ decreased gradually and that of CCl₂F₂ increased up to 90% or higher. These results can be explained by the mechanism involving the secondary ¹³C-selective IRMPD of the primary product CBrClF₂. On the other hand, the carbon-containing product for a CCl₂F₂/Br₂ system was only CBrClF₂; the further IRMPD of which probably regenerated CBrClF₂ in the presence of Br₂. The decomposition probabilities of ¹²C- and ¹³C-containing molecules in both systems were measured as functions of laser line, laser fluence, and reactant pressures.     

Superconductivity in LaPd_2Bi_2 with CaBe_2Ge_2-type structure

正Since the discovery of superconductivity in LaFeAsO_(1-x)F_x,the high-T_c iron-based superconductors have been extensively studied from both experimental and theoretical viewpoints [1-8]. However, the mechanism of the unconventional superconductivity is still to be resolved. To     

Polar optic phonons in Hg2Cl2 and Hg2Br2

Far infrared (30–430 cm^?1) reflectivity measurements of Hg₂Cl₂ and Hg₂Br₂ single crystals have been performed in polarized light. The spectra, which are in agreement with group-theoretical predictions, were analyzed by the oscillator fitting procedure and Kramers-Kronig method. The results are compared with the existing data from other measurements and the large anisotropy of polar modes is briefly discussed. The polarization vectors of all long-wavelength symmetry modes were determined group-theoretically.     

Magnetostriction of SmMn2Ge2 and GdMn2Ge2 intermetallic compounds

Longitudinal and transverse magnetostrictions of polycrystalline samples of intermetallic compounds RMn₂Ge₂ (R=Sm or Gd) are measured in pulsed magnetic fields up to 250 kOe. It is found that linear magnetostrictive strains of about 10^?3 arise in a temperature range in which the magnetic field causes a change in the magnetic state of a manganese magnetic subsystem. The results obtained are described within the model of a two-sublattice ferrimagnet with a negative exchange interaction in the manganese subsystem in terms of a strong dependence of this interaction on interatomic distances.     

Structural,magnetic and neutron diffraction studies on TbFe2-TbAl2, TbCo2-TbAl2 and HoCo2-HoAl2

Both pseudobinary systems exhibit large homogeneous regions of cubic and hexagonal Laves phases. Ordering tendencies on crystallographic sites between Al and the transition metals are observed in the hexagonal type.Electron transfer to the transition metals quenches their moments so that they become nonmagnetic at high Al concentrations. The peculiarities in the mechanism of magnetization which appear in rare earth dialuminides when Al is replaced by a transition metal have been studied in detail at cryogenic temperatures.The first replacement of Al results in a decrease in saturation moment. Neutron diffraction verifies the low ordered rare earth sublattice moments and reveals the ‘lost part’ as a disordered component. Considerable magnetic hardness develops in certain regions of concentration often connected with spontaneous increases in magnetization with field. All available evidence suggests the presence of unusual domain wall effects to be responsible for this effect. High remanences develop in both the hexagonal and in the cubic structures in the intermediate region. The development of disordered magnetic components is connected either with the disorder on crystallographic sites or changes in the free electron concentration.