112型铁基化合物EuFeAs2的单晶生长与表征

铁基超导体中含有一类特殊的112型结构化合物,其层状结构中含有一层锯齿形的As链构型.本文报道了用CsCl助熔剂法生长新型铁基112型EuFeAs₂母体单晶的具体方法,以及对该单晶的结构和物性的详细表征.通过能量色散X射线能谱扫描对单晶样品进行的化学成分分析,以及单晶X射线衍射的结构解析,确定该单晶样品属于EuFeAs₂相,结构精修得到EuFeAs₂具有空间群为Imm2（No.44）的正交晶体结构,晶格常数分别是a=21.285（9）Å,b=3.9082（10）Å,c=3.9752（9）Å.通过低温电阻测量,发现在110 K附近和46 K附近存在两个异常电阻跳变.进一步分析表明,110 K附近存在两个邻近的相变,这两个相变与铁基母体材料中常见的结构相变和Fe²⁺的反铁磁相变相符合.结合磁化率测量分析,可知46 K附近的相变属于Eu²⁺的反铁磁相变.     

Heusler合金Cu2VAl磁性及输运性质的研究

对Heusler合金Cu2VAl多晶甩带样品进行了磁性与输运性质方面的研究.实验发现Cu2VAl在温度T为210K附近发生铁磁-顺磁相变,为弱铁磁体.输运性质的测量表明在7.2K时电阻因局域杂质超导相变而发生突变,电子和声子之间的散射是主要的散射机理.居里温度Tc以下存在侧跃导致的反常霍尔效应,并且7K附近的相变导致霍尔电阻率发生异常.     

Ho2AlFe14Mn2化合物的负热膨胀性质

利用x射线衍射及磁测量手段研究了Ho2AlFe16-xMnx系列化合物的结构.结果表明，该系列化合物具有Th2Ni17型结构；随着x的增加，化合物的单胞体积呈现非线性的变化，结合磁测量结果分析认为，在化合物的磁相变点附近存在较大的正的本征磁致伸缩.在160—285K温度范围内对Ho2AlFe14Mn2化合物进行的变温x射线衍射研究表明，该化合物在其居里点附近(220—270K)具有负热膨胀性质，其平均热膨胀系数为-14×10-4/K. 关键词： Ho2AlFe16-xMnx化合物 负热膨胀 本征磁致伸缩     

单晶NdMnO3的比热研究

研究了低温下NdMnO₃单晶的比热随温度和磁场的变化(2K≤T≤200K，0T≤H≤8T ).对应于 Mn磁矩亚晶格的A型反铁磁(A-AF)相变，零场下的比热曲线在85K附近出现尖锐的λ形峰，随 着磁场的增加，此λ峰降低展宽而且平滑变化，这与此温度附近磁化强度的变化规律一致. 与磁有序相变相关的熵变约为理论值的26％，这可能是由于磁有序涨落延续在较大温区造成 的.在20K以下，比热曲线出现了明显的肩膀形状的Schottky反常，其峰值随着磁场的增加而 逐渐向高温移动.考虑了低温下比热的各种贡献，根据Nd³⁺位有效分子场(H _mf) 引起的Nd^3＋基态双重态(GSD)劈裂对上述现象进行了解释.通过对2K≤T≤2 0K，0Ｔ≤ H≤8T范围内比热数据的拟合，得到了样品的GSD劈裂，德拜温度和A-AF自旋波劲度系数以及 它们对磁场的依赖关系.发现GdFeO₃型八面体旋转引起的A-AF结构中Mn磁矩亚晶 格的铁磁成分可能是H_mf的来源. 关键词： 比热 Schottky反常 反铁磁相变     

非晶态Fe86M4Zr10合金的磁性和电性

本文研究了非晶态Fe₈₆M₄Zr₁₀(M=V,Cr,Mn,Fe,CO,Ni,Cu,B,Si)合金的基本磁性和低温电性,讨论了不同元素M的掺杂对FeZr合金居里温度和磁矩的影响,并用相干交换散射模型解释了样品在居里温度附近出现的电阻率极小。 关键词：     

Heusler合金Cu2VAl磁性及输运性质的研究

对Heusler 合金Cu₂VAl多晶甩带样品进行了磁性与输运性质方面的研究. 实验 发现Cu₂VAl在温度T为210K附近发生铁磁—顺磁相变，为弱铁磁体. 输运性质的 测量表 明在72K时电阻因局域杂质超导相变而发生突变，电子和声子之间的散射是主要的散射机 理. 居里温度T_C以下存在侧跃导致的反常霍尔效应，并且7K附近的相变导致霍 尔电阻率发生异常. 关键词： 磁性 输运 2VAl')" href="#">Cu₂VAl     

时效对Ni-14.5Cr-1.5Si(wt%)合金某些性能的影响

本文研究了Ni-14.5Cr-1.5Si(wt%)合金淬火后时效发生的无序向有序转变对合金电阻率、对铂热电势、比热的影响。结果表明:电阻率显著增加,热电势、比热增加很小。X射线衍射分析表明,这是由于Ni₂Si化合物型δ第二相的形成所致。 关键词：     

Mn掺杂后三元黄铜矿结构半导体CuInTe2的缺陷特征与热电性能

三元黄铜矿结构(也称类金刚石结构)半导体是一类具有热电转换潜力的新型热电材料. 本次工作中采用电负性更小的Mn元素替换CuInTe₂黄铜矿结构半导体中的Cu元素, 设计制备贫Cu化合物Cu_1-xInMn_xTe₂. 研究表明, 当Mn含量较低时, Mn优先占位在In 位置产生受主缺陷Mn_In^-. 因此随着Mn含量的增大, 载流子浓度和电导率均得到改善. 但当Mn含量进一步增大后, Mn可同时占位在In位置和Cu位置, 除产生受主缺陷Mn_In^-外, 还能产生施主缺陷Mn_Cu⁺. 由于两类极性相反的缺陷之间的湮灭现象, 使得缺陷浓度及载流子浓度开始降低, 晶格结构畸变有变小趋势, 因此在高温下晶格热导率仅略有提高. 研究结果表明, 在某一特定的Mn含量(x=0.05)时, 材料具有最优的热电性能(ZT=0.84@810.0 K), 这一性能约是未掺杂CuInTe₂的2倍.     

自旋梯状化合物Sr14(Cu1-yFey)24O41的拉曼散射谱研究

利用常规的固相合成法制备了三种Sr₁₄(Cu_1-yFe_y)₂₄O₄₁(y=0,0.03,0.05)多晶样品,其中y=0.03是单纯Fe³⁺掺杂,y=0.05是Fe³⁺和Fe²⁺混合掺杂.在100—1500cm^-1频移范围内测量了这三种样品的偏 关键词： 拉曼散射 电输运性质 自旋梯状化合物     

NdNi2Ge2化合物的结构和电磁输运性质

利用非自耗真空电弧熔炼法制备了NdNi₂Ge₂化合物样品,采用X射线粉末衍射技术和Rietveld全谱拟合分析方法测定了其晶体结构. 结果显示该化合物的空间群为I4/mmm,点阵参数为:a=4.120(1),c=9.835(0),Z=2,Nd原子占据2a晶位,Ni原子占据4d晶位,Ge原子占据4e晶位. NdNi₂Ge₂化合物呈现顺磁性,应用居里-外斯定律拟合计算得到居里-外斯常数为25.8,居里-外斯温度为6.24 K. 有效势磁矩为3.69μ_B,这与理论计算Nd³⁺的磁矩相符,表明磁矩主要源于Nd³⁺. 电阻率变化范围为0.3 Ω ·μm^-1-1 Ω ·μm,电阻曲线拟合显示NdNi₂Ge₂呈半金属性. 关键词： 2Ge₂')" href="#">NdNi₂Ge₂ Rietveld结构精修 电磁输运     

新型透明导电薄膜ErF3掺杂In2 O3的研制

利用电子束沉积技术首次制备了氟化铒 (ErF₃) 掺杂的氧化铟(In₂O₃)透明导电薄膜(IEFO),研究了薄膜的晶体结构、光学特性和电学特性。利用原子力显微镜测试了不同厚度薄膜的形貌,初步研究了薄膜的生长过程。研究发现:IEFO薄膜为多晶结构,Er原子的掺入改变了薄膜的优势生长方向,使薄膜在(211)、(222)、(444)3个方向上的生长趋势基本相同。 薄膜电阻率为1.265×10^-3 Ω·cm,电子迁移率为45.76 cm²·V^-1·s^-1,电子浓度为1.197×10²⁰ cm^-3,在380~780 nm范围内的可见光平均透过率为81%。     

准一维Cr基超导体RbCr3As3的超导能隙

RbCr₃As₃是具有[（Cr₃As₃）^-]_∞线性链的准一维超导体,超导转变温度约为6.6 K.对RbCr₃As₃单晶进行了电输运和极低温热输运性质的研究.低温下,拟合了RbCr₃As₃正常态电阻率随温度的变化,发现其满足费米液体行为.通过拟合超导转变温度随磁场的关系,得到RbCr₃As₃单晶的上临界场约为25.6 T.对RbCr₃As₃进行了零场下的极低温热导率测量,得到其剩余线性项为7.5 μW·K^-2·cm^-1,占正常态热导率值的24%.测量不同磁场下RbCr₃As₃的热导率,发现与单带s波超导体相比较,RbCr₃As₃剩余线性项随磁场增加相对较快.这些结果表明RbCr₃As₃单晶很可能是有节点的非常规超导体.     

Electronic and magnetic properties of the rare earth intermetallic compounds RRu4Sn6 (R=Nd, Sm, Gd, Tb, Dy and Ho)

A number of compounds of structural formula RRu₄Sn₆ (R=rare-earth element) have previously been reported to form in the tetragonal crystal structure with space group I4¯2m. In this structure the R atoms are well isolated from each other. We embarked on this study to investigate the physical properties and to compare with earlier results obtained on the strongly correlated, low charge-carrier density compound CeRu₄Sn₆. Here we report our results of crystallographic, electrical resistivity, and magnetic studies on this family of compounds. In contrast to the behaviour in CeRu₄Sn₆, magnetic ordering is evident at low temperatures in the compounds with R=Sm, Gd, and Dy, as is evidenced by well-resolved anomalies in the temperature dependence of the electrical resistivity and static magnetic susceptibility.     

Superconductivity in the intermetallic compound YRhAl

The intermetallic compound, YRhAl, has been prepared and is found to be isomorphic with RRhAl (R=Pr, Nd, Gd, Ho and Tm) compounds crystallizing in the orthorhombic TiNiSi-type structure (space group Pnma). Heat capacity and electrical resistivity measurements in the He-3 temperature range reveal that this compound is superconducting with a transition temperature, T_c, of 0.9 K. The electronic specific heat coefficient, γ, and the Debye temperature are found to be 6.1 mJ/mol K and 197 K, respectively. The specific heat jump at the superconducting transition is found to be consistent with the BCS weak-coupling limit. This combined with the earlier observation of superconductivity in LaRhAl (T_c=2.4 K) having a different structure than that of YRhAl, suggests that the underlying structure is not very crucial for the occurrence of superconductivity in RRhAl series of compounds.     

A density-wave-like transition in the polycrystalline V3Sb2 sample with bilayer kagome lattice

Recently,transition-metal-based kagome metals have aroused much research interest as a novel platform to explore exotic topological quantum phenomena.Here we report on the synthesis,structure,and physical properties of a bilayer kagome lattice compound V₃Sb₂.The polycrystalline V₃Sb₂ samples were synthesized by conventional solid-state-reaction method in a sealed quartz tube at temperatures below 850℃.Measurements of magnetic susceptibility and resistivity revealed consistently a density-wave-like transition at Tdw≈160 K with a large thermal hysteresis,even though some sample-dependent behaviors were observed presumably due to the different preparation conditions.Upon cooling through Tdw,no strong anomaly in lattice parameters and no indication of symmetry lowering were detected in powder x-ray diffraction measurements.This transition can be suppressed completely by applying hydrostatic pressures of about 1.8 GPa,around which no sign of superconductivity was observed down to 1.5 K.Specific-heat measurements revealed a relatively large Sommerfeld coefficientγ=18.5 mJ·mol^-1·K^-2,confirming the metallic ground state with moderate electronic correlations.Density functional theory calculations indicate that V₃Sb₂ shows a non-trivial topological crystalline property.Thus,our study makes V₃Sb₂ a new candidate of metallic kagome compound to study the interplay between density-wave-order,nontrivial band topology,and possible superconductivity.     

A-site ordered perovskite CaCu_3Cu_2Ir_2O_(12-δ) with square-planar and octahedral coordinated Cu ions

A novel CaCu_3Cu_2Ir_2O_(12-δ) polycrystalline sample was synthesized at 8 GPa and 1373 K.Rietveld structural analysis shows that this compound crystallizes in an AA'_3B_4O_(12)-type A-site ordered perovskite structure with space group Im-3.Xray absorption spectra reveal a +2-charge state for both the square-planar and octahedral coordinated Cu ions,and the valence state of Ir is found to be about +5.Although the A-site Ca and the A'-site Cu~(2+) are 1:3 ordered at fixed atomic positions,the distribution of B-site Cu~(2+) and Ir~(5+) is disorderly.As a result,no long-range magnetic ordering is observed at temperatures down to 2 K.Electrical transport and heat capacity measurements demonstrate itinerant electronic behavior.The crystal structure is stable with pressure up to 35.7 GPa at room temperature.     

A new layered cuprate superconductor: GaSr2(Y, Ce)2Cu2O9−δ

A new layered cuprate compound with a nominal composition of GaSr₂Y_2−xCe_xCu₂O_9−δ has been prepared. It crystallizes in a tetragonal lattice with cell parameters: a = 3.812 Å, c = 28.16 Å. The structure of the compound belongs to the same family of 1222 phase and is derived from that of GaSr₂LnCu₂O₇ by replacing the single Ln³⁺ layer with a double fluorite (Y, Ce)₂O₂ layer. Like other parent cuprate compounds of superconductors, the as-prepared samples showed antiferromagnetic and semiconducting behavior. After treatment under high oxygen pressure, the samples exhibited bulk superconductivity with transition temperatures between 12–14 K.     

Combined Study of Structural,Magnetic and Transport Properties of Eu_(0.5)Ln_(0.5)BiS_2F Superconductor

Superconductivity below 0.3 K and a charge-density-wave-like(CDW-like) anomaly at 280 K were observed in EuBiS_2F recently.Here we report a systematic study of structural and transport properties in Eu_(0.5)Ln_(0.5)BiS_2F(Ln=La,Ce,Pr,Nd,Sm) by electrical resistivity,magnetization,and specific heat measurements.The lattice constants have a significant change upon rare earth substitution for Eu,suggesting an effective doping.As Ln is changed from Sm to La,the superconducting transition temperature T_c increases from 1.55 K to 2.8 K.In contrast to the metallic parent compound,the temperature dependence of electrical resistivity displays semiconductinglike behavior for all the Eu_(0.5)Ln_(0.5)BiS_2F samples.Meanwhile,the CDW-like anomaly observed in EuBiS2F is completely suppressed.Unlike the mixed valence state in the undoped compound,Eu ions in these rareearth-doped samples are mainly divalent.A specific anomaly at 1.3 K resembling that in EuBiS2F suggests the coexistence of superconductivity and spin glass state for Eu_(0.5)La_(0.5)BiS_2F.Coexistence of ferromagnetic order and superconductivity is found below 2.2 K in Eu_(0.5)Ce_(0.5)BiS_2F samples.Our results supplies a rich diagram showing that many interesting properties can be induced in BiS_2-based compounds.     

Magnetic properties of one-dimensional CoCu(opba) systems and DFT studies of the building blocks

The synthesis of one-dimensional, molecule-based magnets and the investigation of their structure and physical properties are described. The one-dimensional CoCu(opba) system, where opba [ortho-phenylenebis(oxamato)] bridges the metal ions resulted in antiferromagnetic coupling, and was studied by insertion of electron donating and electron withdrawing groups in the organic ligands’ aromatic rings. In order to verify the influence of these modifications, three compounds of the formula [CoCu(opba-xy)], where x=y=CH₃ (compound 1), x=y=Cl (compound 2), x=H and y=NO₂ (compound 3) are described. The electronic structure of the oxamato bridge group has been studied using calculations at the density functional theory (DFT) level for [Cu(opba-xy)]²⁻ building blocks. Magnetic measurements in polycrystalline samples showed ferrimagnetic behavior for the three compounds. Least-squares fits of the experimental data indicate antiferromagnetic couplings J_CoCu of −35.0, −32.9 and −24.2 cm⁻¹ for 1, 2 and 3, respectively.