共查询到19条相似文献,搜索用时 218 毫秒
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X射线衍射实验表明YBa2(Cu0.95M0.05)3O7-δ(M=Ti,V,Cr,Mn,Fe,Co,Ni,Cu和Zn)均为单相结构。Fe,Co,Ni和Zn对Cu的替代使超导临界温度Tc显著下降,而同样含量的Ti,V,Cr,Mn对Cu的替代并未对超导性能产生显著影响。并利用中子衍射分析了Ti,Mn,Fe和Co对Cu原子的取代,发现代换原子对Cu的两个晶位各自存在不同的择优占据
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本文研究了Bi-Sr-Ca-Cu-O体系中理想成份为Bi2Sr2CaCu2O8化合物的超导性能和晶体结构。名义成份为BiSrCaCu2O5.5零电阻超导转变温度Tc(0)=81.5K。用X射线粉末衍射方法测定了Bi2Sr2CaCu2O8的晶体结构,其基本结构属体心四方晶系,空间群为D4h17-l4/mmm,点阵常数a=3.825?,c=30.82?。每单胞化合式单位为2.2Ca占据2(a)等效点系,4Sr,4Bi和4Cu占据三组4(e)位置,其原子参数z分别为0.110,0.302和0.445,16O分别占据8(g),z=0.445和二组4(e),z=0.210和0.380。Bi2Sr2CaCu2O8晶体结构可认为是阳离子沿z轴的(00z)和((1/2)(1/2)z)交错排列,由Aurivillius相导生出来的。讨论了在Bi-Sr-Ca-Cu-O体系中可能存在的其它沿z轴不同堆垛层数的超导相。
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通过测量YBa2Cu3-xMxO7-y(M=Zn,Ni,x=0,0.025,0.05,0.075,0.1,0.15,0.2,0.3)系列样品的晶体结构、正常态电子输运性质、超导电性以及O含量,给出了Zn择优取代Cu(2)的更直接证据;同时,观察到掺Zn系统中的由正交相Ⅰ到正交相Ⅱ的结构相变以及Ni取代Cu带来的电子局域化效应。研究结果表明,具有正二价态的Zn对Cu(2)具有择优取代性,而具有正二价和正三价的Ni并不具有明显的择优取代。对Cu(2)的取代引起超导临界温度的显著变化,但对正常态电子输运性质的影响不明显;对Cu(1)的取代更显著地影响了晶体结构和正常态电子输运性质,同时对Tc产生抑制,我们认为,YBa2Cu307中的高温超导电性以及正常态输运性质是由CU-O平面和Cu-0链共同承担,而Cu-O平面和Cu-0链之间的耦合强度决定着该系统的超导电性的强弱。
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本文用中子飞行时间方法对C-15相的超导材料V2Hf,V2Ta和V2Hf0.8Ta0.2以及V2Zr0.5。Hf0.5和V2Zr0.5Hf0.33Ta0.17的热中子非弹性散射谱作了测量,并计算出相对的广义声子态密度。结果与早先发表的Nb对C-15相V2Zr和V2(Hf0.5Zr0.5)系列声子性能的影响一致:声子频率随超导转变温度Tc增加而软化,随Tc减小而硬化。这表明,对于此类材料弹性软化在一定程度上对提高Tc起了作用。结果还进一步表明V2Zr或V2Hf与V2(Zr0.5Hf0.5)之间有着质的差别,V2Hf加Ta后,Tc增加,声子频率软化,而V2(Zr0.5Hf0.5)加Ta后,Tc减小,声子频率则略有硬化。这与V2Zr和V2(Hf0.5Zr0.5)加Nb的结果是一致的。此结果可以用角动量分波表象的能带论方法分析电-声耦合相互作用得出的杂化理论来定性解释。
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实验研究了Bi2Sr2CaCu2-xSnxO8+δ 的X射线衍射(XRD)和光电子能谱(XPS).实验发现随着掺杂(Sn)量的增加,晶格参数a 和c都有所变化,O1s和Cu2p芯能级谱也发生了变化.实验结果表明: 在低掺杂量时,Sn主要 呈二价态;而在高掺杂浓度时呈四价态;掺Sn对超导电性的影响与其他元素的掺杂不同.这 些实验结果支持化学环境在高温超导样品的电子结构中起着重要作用的结论.
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Bi系超导体
掺杂
X射线衍射
光电子能谱 相似文献
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A. Grusková J. Lipka J. Sláma V. Jančárik M. Papánová M. Štofka A. González G. Mendoza 《Hyperfine Interactions》2006,169(1-3):1223-1230
BaFe12?2x M x Sn x O19 compounds, where M?=?Sn2+, Ni2+ or Zn2+ ions, were synthesized by mechanical milling and partially by citrate precursor methods. Analysis of magneto-crystalline structure has been carried out by Mössbauer spectroscopy. The Sn4+ ions replace Fe3+ ions on 2b and slightly on 2a?+?4f1 sites, Zn2+ ions strongly prefer 4f1 sites, Sn2+ ions prefer 4f1 sites too and Ni2+ ions occupy 4f2 and 12k or 2a sites. The magnetic properties were evaluated by the vibrating sample magnetometry and the thermomagnetic analysis. A large variation of the intrinsic coercivity H c (330 to 78 kA/m) and of temperature coefficient of coercivity of ΔH c /Δ? (0.39 to 0.22 kA/m°C) were achieved as a function of the (Zn–Sn) and (Sn–Sn) substitutions, respectively. The Curie temperature T c decreased with the (Ni–Sn) substitution from 447 to 399°C. 相似文献
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57Fe and119Sn Mössbauer spectroscopy as well as X-ray diffractometry were used to study Ti?Ca?Ba?Cu?O high Tc superconductors (Tc=106K) in the 4 to 300 K temperature range. X-ray diffractograms showed the dominant phase of these supercondutors to be 2-1-2-2 type. Three main iron sites were found and associalted with Fe in Cu sites in the real crystal. The dopublet with IS=0.25 mm/s and QS=0.7 mm/s at RT was attributed to the regular Cu site. No magnetic splitting was observed either in Sn or in Fe spectra taken even at 4 and 5K. 相似文献
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I. Felner I. Nowik E. R. Bauminger U. Yaron D. Hechel 《Hyperfine Interactions》1992,70(1-4):1163-1166
57Fe Mössbauer spectroscopy, magnetic susceptibility and powder x-ray-diffraction measurements were used to study superconductivity and magnetic order in YBa2(Cu1?xFex)4O8+δ. Tc is decreasing with x, disappearing for x>xc≈0.04. For xc iron substitutes Cu, predominantly in the Cu(1) site exhibiting a single quadrupole Mössbauer spectrum at 90 K. For x>xc magnetic order is observed in the Cu(2) site, TN=380 (5) K for x=0.1 and Heff (Cu(2), 4.2 K)=510(2) kOe. However, the most surprising discovery is that for x=0.025, for which Tc=27(2) K, the Fe in the Cu(1) site orders magnetically at TN=30(2) K and Heff (Cu(1), 4.2 K)=461(2) kOe. The coexistence and competition between superconductivity and magnetic order in the Cu(1) and Cu(2) sites in YBa2Cu4O8 are discussed in terms of the previously observed phase diagrams for Y1?xPrxBa2(Cu1?yFey)3Oz. 相似文献
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The magnetic properties of intermetallic compounds RMn6Sn6 (T=Gd and Y) have been investigated by119Sn Mössbauer effect measurements. The differences of the hyperfine field on both the Sn1 and Sn3 sites were small between GdMn6Sn6 and YMn6Sn6, while the Mn sublattice orders ferromagnetically for R=Gd and antiferromagnetically for R=Y. This result indicated that Mn moments order antiferromagnetically in the intra-plane of the Kagomè net in YMn6Sn6. 相似文献
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K. Kumagai Y. Nakamichi Y. Nakamura I. Watanabe H. Nakajima T. Fujita 《Hyperfine Interactions》1989,50(1-4):583-591
Nuclear quadrupole resonances (NQR) of139La in La2−xMxCuO4 (M=Ba, Sr) and63Cu in YBa2CU3O7 have been investigated with substitution of Cu by magnetic impurities. For La-system, the strong enhancement of the nuclear
relaxation rate, 1/T
1 atT
c
*≈10 K (suggesting the occurrence of magnetic instability with hole-doping), is suppressed by 3D-antiferromagnetism induced
by magnetic impurities. In the superconducting region, fluctuations of Cu moments at low temperatures remain extremely fast
as at high temperatures. For Y-system, Fe-ions are substituted for both Cu(1) and Cu(2) sites, But Co-ions are preferentially
substituted to Cu1 sites. The peaks in the relaxation rate of Cu indicate the appearance of magnetic ordering without destroying
superconductivity for the 0.5%-Fe doped sample. 相似文献
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在三方铁电(FE)-四方反铁(AFE)的准同型相界附近制备了一系列组份为(Pb0.97La0.02)(Zr1-x-ySnyTix)O3(x=0.09或0.1;0.16≤y≤0.38)的反铁电陶瓷.研究了Sn含量y对电场诱导AFE→FE相变电场Ec、反铁电双电滞回线损耗ΔE、以及温度诱导FE→AFE相变温度TFE,AFE→顺电(PE)相变温度Tc的影响.沿AFE-FE相界Ti含量一定的条件下,Ec随着Sn含量y的增加而增大,ΔE减小,TFE与Tc均降低.场诱相变的回线参量Ec,ΔE与相变温度TFE和Tc相关联.在直流偏压下用原位X-射线衍射表征了相变时晶格结构的变化,结果表明,当电场达到AFE→FE相变临界场时,伴随相变的发生,晶格结构由四方相转变为三方相,晶胞体积增大.
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