共查询到20条相似文献,搜索用时 973 毫秒
1.
Thermoelectric power measurements are reported for seven samples with different x in the Gd1.85-xSmxCe0.15CuO4 system at temperatures ranging from 80K to 300K. For Sm-rich superconducting samples, thermoelectric power S has a small negative value and is almost temperature independent. As the content of Sm decreases, the absolute value of S increases and a broad valley appears in the S(T) curve. The results which can be interpreted in terms of a two-channel model support the existence of mid-gap states with Fermi level close to the minimum of the density of states as well as the coexistence of electron and hole carriers. It is suggested that a linear temperature dependence of S with a small negative slope is close to the intrinsic behavior in the a-b plane of normal states for superconducting samples. 相似文献
2.
K. Bohmhammel G. Wolf N.E. Alekseevskii E.P. Krasnoperov 《Solid State Communications》1977,21(6):519-520
Heat capacity of the Nb3Al0.8Ge0.2 samples have been measured in the temperature range 14–25K. It has been shown that the electron part of the heat capacity (γ) and the Debye temperature undergo only a small change after thermal treatment leading to significant increase of superconducting Tc. Such an increase of the band density of states N(EF)band may be caused by appropriate changes of phonon spectrum. The character of these changes is determined, to a great extent, by localization of the d-electrons in the niobium chains. 相似文献
3.
T. Tamegai Y. Nakajima Y. Tsuchiya A. Iyo K. Miyazawa P.M. Shirage H. Kito H. Eisaki 《Physica C: Superconductivity and its Applications》2009,469(15-20):915-920
We have prepared iron-oxypnictide SmFeAsO1−xFx by ambient-pressure technique and SmFeAsO1−y by high-pressure technique, and characterized their bulk and local magnetic properties by using SQUID magnetometer and magneto-optical imaging. While the high-pressure samples have densities close to the theoretical value, the ambient-pressure samples have several small voids. Despite these structural differences between the two kinds of samples, they both have superconducting transition temperature above 50 K. In addition, magneto-optical images for both samples show similar kinds of inhomogeneities with large current concentrated in several grains and with small intergranular current. The estimated intragranular currents for both samples are over 105 A/cm2 at low temperatures and low fields. 相似文献
4.
5.
H MatsuiT Sato S NishinaT Takahashi Y MiharaY Hata K KadowakiT Mochiku 《Journal of Physics and Chemistry of Solids》2002,63(12):2329-2332
We have performed high-resolution photoemission spectroscopy (PES) on FeSr2YCu2O7+δ, of which superconductivity of Tc=49 K was recently reported. We clearly observed opening of a d-wave-like superconducting gap and estimated the maximum gap value (Δmax) to be 10 meV at 15 K. This gap value gives 2Δmax/kBTc∼5, suggesting a strong-coupling nature of superconductivity in FeSr2YCu2O7+δ. Comparative PES study with superconducting and insulating samples shows that the valence band is rigidly shifted as a function of doping without evolution of additional states within the insulating gap. 相似文献
6.
K. Re?ko L. Dobrzyński A. SenyshynH. Fuess K. SzymańskiB. Yu Kotur W. Suski 《Journal of magnetism and magnetic materials》2011,323(14):1860-1867
The crystallochemical and magnetic nature of ternary Sc1+δFe4−δAl8 intermetallic with a small Sc excess δ=0.1 was investigated by scanning electron microscope, X-ray powder diffraction, neutron diffraction, Mössbauer effect and superconducting quantum interference device techniques. The sample crystallizes in a tetragonal ThMn12 type structure. The excess of Sc atoms substitute Fe at the (8f) positions and have a pronounced effect on the magnetic properties. The experiments carried out in temperature range 4-320 K show that below 120 K the magnetic structure of the alloy forms a double cycloid with magnetic moments rotating according to the incommensurate in-plane wave vector, which is temperature independent up to 160 K. The value of Fe magnetic moment is close to 0.9 μB atom−1 at 4 K. Temperature dependence of unit cell dimensions can be explained within the Debye-Grüneisen approximation. 相似文献
7.
The DC and AC conductivities of samples from the system (As2S3)100−x(AsSe0.5Te0.5I)x, where x=0, 5, 10, 15, 20, 25, 30, 35, 50, 70 and 90 mol%, were measured as a function of temperature. Besides, the AC conductivities of the samples with x=10 and 30 were measured as a function of frequency from room temperature to the glass transition temperature. The DC conductivity dependence on temperature is of the Arrhenius type, whereas the value of the pre-exponential factor suggests the electrical conduction by localized states in the band tails and by localized states near the Fermi level. The small values of the conduction activation energy (10−2-10−1 eV) obtained at higher frequencies suggest that the conduction in these materials is due to hopping of charge carriers between close defect states near the Fermi level. 相似文献
8.
测量了块体金属玻璃Zr46.75Ti8.25Cu7.5Ni10Be27.5在退火前后其电阻值随温度的变化,测量的温度范围为1.5—300K.样品在退火前后都发现有超导现象.零磁场下其超导转变温度Tc分别为1.84和3.76K.在5—300K温度范围内,原始样品具有负的电阻温度系数.如果取Zr, Ti, Cu, Ni及Be分别贡献出1.5, 1.5, 0.5, 0.5及两个传导
关键词:
块体金属玻璃
超导
电阻温度系数 相似文献
9.
Bulk superconducting La2CuO4+δ single crystals are obtained by using electrochemical intercalation technique from the as-grown insulating samples. Oxidation is carried out by constant current I=10μA at temperature T=70℃ and room temperature, respectively. Structure and magnetic properties are studied by low-temperature X-ray diffraction and susceptibility measurements. A superconducting phase with Tc of 19K and δ-0.12 can be attributed to the formation of oxygen clusters. Room temperature oxidation is inhomogeneous: two superconducting phases with Tc1 of 24K and Tc2 of 8K and an antiferromagnetic phase are coexisting in the crystal. It is found that the appearance of Tc in this system has the "step" tendency. 相似文献
10.
11.
Yanpeng Qi Xianping ZhangZhaoshun Gao Zhiyu ZhangLei Wang Dongliang WangYanwei Ma 《Physica C: Superconductivity and its Applications》2009,469(13):717-720
Nb-sheathed Sr0.6K0.4Fe2As2 superconducting wires have been fabricated using the powder-in-tube (PIT) method for the first time and the superconducting properties of the wires have been investigated. The transition temperature (Tc) of the Sr0.6K0.4Fe2As2 wires is confirmed to be as high as 35.3 K. Most importantly, Sr0.6K0.4Fe2As2 wires exhibit a very weak Jc-field dependence behavior even the temperature is very close to Tc. The upper critical field Hc2(0) value can exceed 140 T, surpassing those of MgB2 and all the low temperature superconductors. Such high Hc2 and superior Jc-field performance make the 122 phase SrKFeAs wire conductors a powerful competitor potentially useful in very high field applications. 相似文献
12.
T.H. Meen W.R. Chen L.W. Ji C.J. Huang 《Journal of Physics and Chemistry of Solids》2007,68(7):1390-1395
Polycrystalline samples of electron-doped Pr1.85Ce0.15CuO4+δ have been prepared under different annealing conditions and investigated by means of X-ray-diffraction, oxygen content analysis, electrical resistivity, magnetic susceptibility and low temperature specific heat measurements. X-ray-diffraction patterns show that samples contain a single T′ phase. The superconducting transition temperatures Tcm taken with the onset of diamagnetism in magnetic-susceptibility measurements are 20 and 19.5 K for sample annealed in flowing Ar gas and in vacuum (∼10−3 torr), respectively. The data of the samples, which are annealed in flowing Ar gas, show clear evidence for an αT2 term at zero magnetic field in superconducting electronic specific heat, and are consistent with d-wave superconductivity. However, this behavior is not observed in the other sample, which is annealed in vacuum. These results indicate that different heat treatments affect the oxygen content, homogeneity, superconducting transition temperature Tc, superconducting volume fraction, and the superconducting pairing symmetry of Pr1.85Ce0.15CuO4+δ. 相似文献
13.
Mahuya ChakrabartiA. Sarkar S. ChattapadhayayD. Sanyal A.K. PradhanR. Bhattacharya D. Banerjee 《Solid State Communications》2003,128(8):321-324
The temperature dependent (30-300 K) Doppler broadening of the positron annihilated γ-radiation measurement has been investigated on single crystalline Bi2Sr2CaCu2O8+δ (Bi-2212) high Tc superconducting samples along two different crystallographic orientations. It has been observed that throughout the temperature range the electron momentum distribution has a larger value along the crystallographic c-axis than in the a-b plane. The temperature dependent Doppler broadened positron annihilation γ-radiation lineshape analysis shows a step like increase of S-parameter at the temperature region 92-116 K. 相似文献
14.
We have measured the resistivity of NbSe3 doped with 5% Ta from room temperature down to 0.5K and compared our results with similar measurements on pure NbSe3. The pure sample remains normal to the lowest temperature (0.5K), whereas the doped sample has a sharp transition to the superconducting state with Tc = 1.5 ± 0.2 K. Measurements of the critical magnetic field indicate that the Ta doped samples are homogeneous, anisotropic three dimensional superconductors. 相似文献
15.
The Hall coefficient, thermoelectric power and electrical resistivity of the liquid quenched amorphous Mg80.4Cu19.6 alloy have been measured over a wide temperature range below room temperature. The 2kF value deduced from the observed Hall coefficient agrees well with the free electron value. The thermoelectric power is positive and increases linearly with increasing temperature above approximately 180 K. The downward deviation is evident in the lower temperature range. This behaviour is in sharp contrast with the negative thermoelectric power observed in the amorphous Mg-Zn alloy. Nevertheless, the overall temperature variation of the electrical resistivity resembles the previously reported data of the amorphous Mg72.5Zn27.5 alloy in various aspects; (1) the room temperature resistivity value, (2) the negative TCR and its magnitude, (3) the appearance of a broad maximum at about 50 K and a minimum at about 10 K and (4) T2-dependence in the range of 10~30 K and -dependence in the range of 50~220 K. The results are discussed in connection with criterion and Mooij correlation. 相似文献
16.
Ferromagnetic shape memory alloy with nominal composition Co37Ni34Al29 is investigated by transport and magnetic measurements. The anomaly due to the martensitic transition is observed around 130-210 K. The thermal hysteresis, observed due to martensitic transition in the dc magnetization versus temperature data, gets suppressed at higher applied field. Below 50 K, magnetization varies with temperature perfectly as T3/2, which signifies that spin wave excitations are largely responsible for thermal demagnetization. The sample shows small negative magneto-resistance, which varies non-monotonically with temperature showing largest value at around 200 K. 相似文献
17.
18.
The superconducting transition temperature Tc1 and the reentering temperature Tc2 to the normal ferromagnetically ordered state in the system ErcY1?cRh4B4 were determined as a function of the concentration of Er. Comparing our results with the recent theory of Maekawa et al., the exchange interactions J′ among local spins and I between local spins and superconducting electrons were estimated as J′ ? 0.30 K and I2N(0) ? 0.046 K, where N(0) is the density of states. A sudden decrease of Hc2 at Tc2 was observed in a high concentration region suggesting the first order transition. 相似文献
19.
用固相反应法合成了名义组分为Bi1.92Pb0.32Sr2Ca1.7Mg0.3Cu3.07Ox的块状样品。X射线衍射谱(XRD)、扫描电子显微镜(SEM)和电子探计X射线分析(EDAX)结果以及块状和粉状试样的交流磁化率测量表明,样品中存在110和85K两个超导相;2223相(110K)首先在2212相(85K)晶体的晶界和外部区域生成。本文认为,最初存
关键词: 相似文献
20.
A. Sugimoto K. Shohara T. Ekino Y. Watanabe Y. Harada S. Mikusu K. Tokiwa T. Watanabe 《Physica C: Superconductivity and its Applications》2009,469(15-20):1020-1023
Scanning tunneling microscopy/spectroscopy (STM/STS) measurements on multi-layered cuprate superconductor Ba2Ca5Cu6O12 (O1−x Fx)2 are carried out. STM topographies show randomly distributed bright spot structures with a typical spot size of 0.8 nm. These bright spots are occupied about 28% per one unit cell of c-plane, which is comparable to the regular amount of apical oxygen of 20% obtained from element analysis. Tunneling spectra simultaneously show both the small and the large gap structures. These gap sizes at 4.9 K are about Δ 15 meV and 90 meV, respectively. The small gap structure disappears at the temperature close to TC, while the large gap persists up to 200 K. Therefore, these features correspond to the superconducting gap and pseudogap, respectively. These facts give evidence for some ordered state with large energy scale even in the superconducting state. For the superconducting gap, the ratio of 2Δ/KBTC = 4.9 is obtained with TC = 70 K, which is determined from temperature dependence of the tunneling spectra. 相似文献