共查询到18条相似文献,搜索用时 203 毫秒
1.
研究了Gd1-xCaxBa2Cu3O7-y(0.0≤X≤0.20)高温超导体在常压和高压下的超导电性在1-300K温度范围内,利用Bridgman对顶砧获得压力达9.0GPa,测量了(X=0.10,0.15,0.20)样品的dTc/dp分别为7.68,7.8和4.46K/GPa。发现Tc的压力导数随着ca2+含量的增加而下降,分析了氧含量对Tc和dTc/dP的影响.利用常压下晶格参数精修值和阳离子与氧离子间距随压力的改变,说明CuO2面在超导电性上的作用,用CuO2面之间耦合解释Tc(P)曲线的非线性关系。
关键词: 相似文献
2.
对Y-系(123)相超导材料的微波焊接进行了初步研究,结果表明微波快速焊接后的试样,经960℃空气中退火15h后炉冷,其Tc可恢复至89.7K,比焊接前试样的Tc低1.6K。利用电子探针对焊接前后样品的显微结构进行了比较,发现焊区组织致密,但在后处理过程中超导相发生了再结晶,导致焊缝变宽,气孔因聚集而变大。同时用电子微探针分析仪发现,焊接后焊区普遍存在Y2BaCuOx相、Ba2-yCuy
关键词: 相似文献
3.
研究了掺Ba对Bi2Sr2-xBaxCaCu2Oy(0≤x≤0.15,0.3)单晶和多晶样品超导电性的影响,结果表明,有少量Ba2+离子进入了超导相,且有固溶度极限.对于2212相单晶,c轴参数和Tc均随Ba含量增加而增加;对于慢冷多晶样品,掺Ba可明显提高Tc;然而对于淬大多晶样品,Tc没有明显变化,用掺Ba
关键词: 相似文献
4.
5.
在较宽的温度(4.2-80K)和磁场(0-8T)范围内测量了YBa2Cu3O7-δ和Y0.9Eu0.1Ba2·Cu3O7-δ样品的磁滞回线和磁弛豫,研究了其M(t),Jc(T)和Ueff(J)关系,并与现有的一些理论模型所预言的结果进行了比较。结果表明:(1)与YBa2Cu3O7-δ相比,Y0.9Eu0.1·Ba2Cu3O7-δ样品的有效钉扎势和无磁通蠕动时的临界电流密度有明显提高,表明Eu的部分替代引入了新的、具有更大的钉扎势的钉扎中心;(2)与其它模型相比,集体钉扎——蠕动理论对我们的实验结果作了更好的描述,因而本文为这一理论提供了新的实验证据。
关键词: 相似文献
6.
7.
通过制备(YBa2Cu3O7)1-x(V2O5)x(0≤x≤0.15)复合材料,获得了一系列典型的弱连接的颗粒超导体,其中以dR/dT-T关系中呈现出双峰转变为主要特征。第一峰代表晶粒的超导转变,第二峰代表颗粒系统超导长程序的形成。对于具有双峰转变的样品,其临界电流密度一致地符合ic~(1-t)n,n=1.6.这一行为与三维Josephson结网络系统的渗流行为相一致;对于不具有双峰转变的系统,临界电流密度随温度的变化尽管也可以用jc~(1-t)n描述,但是幂指数n明显地大于1.6,且随样品的不同而离散地分布。本文还对产生这种离散的原因进行探索和分析。
关键词: 相似文献
8.
9.
10.
用第一原理的LDF-LMTO-ASA超元胞法,模拟由X射线吸收谱精细结构测定的BaBiO3中,Bi有两种价态Bi3+和Bi5+及与之相应的两种不同键长的Bi—O八面体,以及K掺杂对晶体结构的影响.计算了Ba4Bi4O12,(Ba3K)Bi4O12,(BaK)Bi2O6,(BaK3)Bi4O12,K2Bi2O6(简记为(404),(314),(112),(134),(022))五种“样本”的电子结构.结果表明,(404)和(314)分别为Eg=1.6eV及Eg=1.5eV的半导体,其它“样本”为金属.总能的分析表明(134)是不稳定的,故溶解极限为x=0.5.以“取样”方式按伯努利分布确定任意组分各“样本”的概率,进而计算了(Ba1-xKx)BiO3电子结构随组分的变化.最后用逾渗模型说明了超导转变温度Tc在x=0.25附近的突变
关键词: 相似文献
11.
Wolf E. L. 《Superlattices and Microstructures》1996,19(4):305-312
It is clear that many of the cuprate superconductors are truly superlattices, composed of sheets whose individual superconducting critical temperatures may approach bulk values. Such a cuprate is Bi2Sr2CaCu2O8, often referred to as BSCCO-2212. Scanning tunneling spectroscopy (vacuum tunneling) applied toa-bBiO cleavage planes ofTc≈90 K BSCCO single crystals under liquid helium simultaneously provides topography and local dI/dVspectra (superconducting density of states: DOS). The spectra, which are similar to those obtained from angle-resolved photoemission spectroscopy, confirm a large gap parameter Δ(x,y) on the uppermost layer. The dI/dVspectra do not unequivocally select order parameter symmetry, but are probably consistent with d-wave or anisotropic s-wave states. Spatial variations of Δ on a 100 Å scale are attributed to variation in BiO metallicity, originating in oxygen stoichiometry variations. A model is presented to explain the different dI/dVspectra which are seen, and associated with different local oxygen concentrations. This model, based on the superconducting proximity effect, assumes that in some regions the BiO uppermost layer is insulating and in other regions it is metallic, in the latter case induced superconductivity by proximity to the CuO2planes. Our STM measurements appear to sample only the uppermost half cell of the crystal, and contain no obvious superlattice features. Recent measurements have confirmed Josephson radiation from voltage biasedc-axis pillars of BSCCO. From the point of view of the present work, the superconducting systems which weakly couple along thec-direction to create Josephson junctions are probably half-cell slabs of height 15.4 Å, each containing two CuO2and two BiO layers, which act as single composite electrodes for the Josephson junctions. 相似文献
12.
F.G. Aliev N.B. Brandt V.V. Moshchalkov S.M. Chudinov 《Solid State Communications》1983,45(3):215-218
Resistivity measurements of CeCu2Si2 are carried out under pressures p up to 12 kbars. Unlike polycrystalline samples, no traces of superconductivity have been observed in CeCu2Si2 at ambient pressure. When pressure is applied, CeCu2Si2 monocrystals become superconducting with anomalously large ratio Hc2(0)/Tc (0) = 34 K0e/K and with the derivative dHc2/dT(T=Tc) = 140 K0e/K 相似文献
13.
We have studied the electrical and infrared properties of Bi2Sr2Ca1Cu2O8 compound in three states. Electrical and IR measurements show that the pure powder state sample is a semiconductor, the ceramic Bi2Sr2Ca1Cu2O8 sample prepared after annealing at 820°C for 240 hours shows a Tc of 85 K, whereas Bi2Sr2Ca1Cu2O8 sample prepared through glassy route, i.e. melting at 1250°C and annealing at 820°C for 240 hours shows a drop of Tc by 5 K. The infrared spectra of superconducting ceramic and glass ceramic states in the available frequency range of measurement reveals the presence of three phonons. Since the vibrational mode around 595 cm–1 is due to CuO2 layers and as the CuO2 layers are responsible for Tc in the ceramic superconductors, any change in these layers will affect the Tc. The shifting of the 595 cm–1 mode towards lower frequencies in the glass ceramic due to different preparation process, indicates that there is a change in CuO2 layers resulting in a change of Tc, which is confirmed by Four probe dc measurements. 相似文献
14.
对高品质单相多晶Bi2Sr2CaCu2O8+δ样品作真空或H2气氛中不同温度下的热处理。由X射线结构分析,其正常态和超导态性质(特别是载流子浓度)的系统测量结果表明:Bi2Sr2CaCu208+δ样品在H2气氛中热处理,其氧的释放可分为两个阶段:一是Bi-O层之间的过量氧原子的逸出,降低系统的载流子浓度,从而调节Tc;二是CuO2面内氧原子的迁移,产生氧空位,使CuO2面内Cu2+的短程二维反铁磁(2D-AFM)有序背景遭到破坏。可以认为:以往文献中报道的Bi2Sr2CaCu2O8+δ超导体的吸氢效应导致Tc的变化,很可能主要的并不是氢原子的电子掺杂行为,而是与吸氢过程中氧含量的变化相联系。
关键词: 相似文献
15.
Porous magnesium diboride samples have been prepared by the heat treatment of a pressed mixture of Mg and MgB2 powders. It was found that linked superconducting structure is formed down to the minimum normalized density γc=d/d0≅0.16 (percolation threshold), where d is the density of MgB2 averaged over the sample, d0=2.62 g/cm3 is the X-ray density. Lattice parameters and critical temperature of the porous sample decrease with increasing porosity (decreasing γ) and Tc2≅32 K is minimal at γc. The grain boundaries in the porous samples are transparent for the current and Jc∼3×105 A/cm2 in self field at T=20 K in the samples with γ∼0.24. 相似文献
16.
Y. V. Piskunov K. N. Mikhalev Yu. I. Zhdanov A. P. Gerashenko S. V. Verkhovskii K. A. Okulova E. Yu. Medvedev A. Yu. Yakubovskii L. D. Shustov P. V. Bellot A. Trokiner 《Physica C: Superconductivity and its Applications》1998,300(3-4)
and
NMR measurements in the normal and superconducting states of Tl2Ba2Ca2Cu3O10−δ with different δ are reported. In the overdoped Tl2223 sample with Tc=117 K (Tcopt=123 K) and δ1<δopt different temperature dependencies of the Knight shift
are revealed for inequivalent CuO2 layers. For the inner CuO2 layer with the square oxygen coordination of Cu the decrease of
with temperature is more gradual. In going towards the underdoped Tl2223 with Tc=104 K and δ2>δopt the changes of
with temperature are found to be the same for both types of copper layers. The quadrupole coupling constants for copper and oxygen from different CuO2 layers were obtained. From the variations with doping of the valence contribution to the electric field gradient at copper sites, we estimate both the hole numbers at Cu and oxygen sites and the real concentration of mobile hole carriers nh in each of inequivalent CuO2 layers. In the overdoped Tl2223 sample the charge density in the inner layer differs from the one in the outer plane (with five-fold oxygen coordination for Cu). Our results show that the inhomogeneity of the charge distribution disappears in the underdoped regime. The results are compared with calculations of the charge distribution among the CuO2 planes in multilayered cuprates reported by Haines and Tallon [E.M. Haines, J.L. Tallon, Phys. Rev. B 45 (1992) 3127]. 相似文献
17.
V.N. Nguyen F. Tcheou J. Rossat-Mignod R. Ballestracci 《Solid State Communications》1983,45(2):209-213
Neutron diffraction studies and magnetic measurements on the compounds TbNi2Si2 (1), HoCo2Si2 (2) and TbCo2Si2 (3) revealed a collinear antiferromagnetic order below TN = 10 ± 1 K (1), TN = 13 ± 1 K (2) and TN = 30 ± 2 K (3) with the rare earths moments oriented along the c-axis [m0 = 8.8 ± 0.2 μB (1), m0 = 8.1 ± 0.2 μB (2), m0 = 8.8 ± 0.2 μB (3)] and the corresponding wavevector are . The magnetic structure of the compounds HoCo2Si2 and TbCo2Si2 consists of ferromagnetic layers perpendicular to the c-axis coupled antiferromagnetically (+?+?) while for TbNi2Si2 the ordering within (0 0 1) plane is antiferromagnetic and the planes (0 0 1) are indeed decoupled. 相似文献