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1.
We have investigated the superconducting properties of the Bi1.7 Pb0.3Sr2Ca2−xCe
x
Cu3O10+δ system with x=0.00, 0.02, 0.04, 0.08 and 0.1 by X-ray diffraction and magnetic susceptibility. The substitution of Ce for Ca has been found
to drastically change the superconducting properties of the system. X-ray diffraction studies on these compounds indicate
decrease in the c-parameter with increased substitution of Ce at Ca site and volume fraction of high T
c (2 : 2 : 2 : 3) phase decreases and low T
c phase increases. The magnetic susceptibility of this compound shows that the diamagnetic on set superconducting transition
temperature (onset) varies from 109 K to 51 K for x=0.00, 0.02, 0.04, 0.08 and 0.1. These results suggest the possible existence of Ce in a tetravalent state rather than a trivalent
state in this system; that is, Ca2+ → Ce4+ replacement changes the hole carrier concentration. Hole filling is the cause of lowering T
c of the system. 相似文献
2.
Electron-doped (Ba1−x
La
x
)MnO3 compounds were prepared for x=0−0.5. Measurements of X-ray diffraction (XRD) at room temperature and temperature variation of dc electrical resistivity
down to 20 K were carried out. Samples with x=0.2–0.5 exhibit metal-insulator (M-I) transition. The maximum M-I transition temperature (T
c) of 289 K was observed for 30% of La doping (x=0.3). XRD patterns of these samples (x=0.2−0.5) were analyzed using Rietveld refinement. These samples are found to be mostly in single-phase form with orthorhombic
symmetry (space group Pbnm). We have found strong correlation between Mn-O-Mn bond angles and T
c of M-I transition. The resistivity data below T
c could be fitted to the expression ρ=ρ
1+ρ
2
T
2 and this shows that double exchange interaction plays a major role even in Mn4+-rich compound. Above T
c the resistivity data were fitted to variable range hopping and small polaron models. 相似文献
3.
It is shown that by adopting a very gradual programmed cooling procedure in oxygen environment one can obtain a sharp transition
(ΔT
c⋍1 K) in YBa2Cu3O7−x
while retaining the high-T
c value (⋍105 K) of samples prepared by a semi-wet route. This is attributed to a maximum occupancy of oxygen at 0 1/2 0 sites
and a near-perfect ordering of vacancies at 1/2 0 0 sites in the orthorhombic unit cell which maximizes the availability of
conduction paths in the form of continuous CuO4 chains. Critical current densities (J
c) of 204 A cm−2 are obtained for bulk samples at 77 K. It is suggested that the intergrain coupling is weak and thus limits the transportJ
c-values. 相似文献
4.
Variation of the copper concentration in the nominal composition YBa2Cu3±x
O7−δ markedly influences the superconducting transition. The transition occurs at the highest temperature with lower width, whenx = +0·25.
Communication No. 82 from Materials Research Laboratory. 相似文献
5.
The superconducting transition temperature of the highT
c compound Y1Ba2Cu3O7−x
does not show degradation consequent upon the addition of metallic silver up to a concentration of 60 wt per cent. The X-ray
diffraction data confirm that the oxygen deficient distorted orthorhombic perovskite structure of the pure compound stays
intact as if silver does not enter the crystal lattice. SEM studies do show the presence of silver at the grain boundaries
only. Silver is found to restrict the grain growth. 相似文献
6.
N Venkataramani K Muralfedharan A Datta S N Bhatia OM Prakash C M Srivastava 《Pramana》1988,30(5):L455-L457
Zr and Ti have been substituted in the system Y1−x
M
x
Ba2Cu3O7−δ(M=Zr, Ti,x=0.05,0.1). We find that theT
c value is unchanged, ∼90K for Zr substitutions up to 10% and in the case of Ti substitutions theT
c drops significantly. These changes may arise from their site preference. 相似文献
7.
Fan Yu-shan Song Hong-zhang Li Zhi-hui Yang De-lin Hu Xing 《Frontiers of Physics in China》2006,1(3):368-370
The oxygen adsorption-desorption properties of RBa2Cu3O7−δ
(R = Gd, Er, Eu, Dy, Sm, Ho and Nd) and Y1−x
LaxBa2Cu3O7−δ
(x=0.1, 0.5 and 1.0) were investigated from room temperature to 950 °C by thermogravimetry (TG). The results show that all samples
will release oxygen with the increasing of temperature and the released oxygen can be absorbed back into the sample when temperature
decreases. However, dependent on the rare earth element, the amount of the released oxygen is different for these samples.
Moreover, in the temperature increasing and decreasing circle the repetition of oxygen adsorption-desorption is also different. 相似文献
8.
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
9.
Measurements of the coefficient of linear thermal expansion α have been carried out for the orthorhombic and tetragonal phases
of RE1Ba2Cu3O
y
(RE=Y, Gd, Dy) compounds using a high resolution capacitance dilatometer in the temperature range 77–300 K. All the superconducting
samples exhibit a jump Δα at their respective transition temperatures,T
c. Evidences of, sample-to-sample variation in α values and dependence of Δα on the sample preparation conditions, have been
obtained. The non-superconducting samples, in general, exhibit lower values of α possibly because of lowering of oxygen content. 相似文献
10.
B K Basu S M Pattalwar R N Dixit S Y Shete A K Rajarajan L C Gupta R Vijayaraghavan 《Pramana》1988,30(4):L367-L370
We report here the results of our heat capacityC
p measurements on a monophasic material HoBa2Cu3O7−y
. ΔC
p/Tc, the jump inC
p at the superconducting transition temperature (=91 K) of the material is measured to be 31 mJ/mol-K2. 相似文献
11.
R. Kita N. Hosoya N. Otawa S. Kawabata T. Nakamura O. Miura M. Mukaida K. Yamada A. Ichinose K. Matsumoto M.S. Horii Y. Yoshida 《Physica C: Superconductivity and its Applications》2009,469(15-20):1157-1160
We investigated the effects of added Tm2O3, Sc2O3, and Yb2O3 on the superconducting properties of sintered Er123 samples. Tm2O3 addition caused the least Tc degradation, exhibiting a Tc above 90 K even for 17 vol% addition. Samples with added Sc2O3 maintained a Tc at above 90 K up to an addition of 7.2 vol%, while Yb2O3-containing samples showed a monotonic decrease in Tc with increased vol% of added Yb2O3. Tm2O3-containing samples exhibited a slight increase in Jc(0.1 T)/Jc(0) and had constant Jc values even for 17 vol% addition. XRD and SEM results indicate that the Tm2O3 is very stable in the superconducting matrix. 相似文献
12.
Europium oxide (Eu2O3) substituted compound has been prepared by solid-solid reaction of the powders of Eu2O3, BaCO3 and CuO at 950°C for 16 hours. The thin films have been deposited by high vacuum evaporation technique (vacuum ≈ 10−6 torr). The variation of current (I) with voltage (V) at room temperature (RT) i.e. 294 K and in ice (273 K) are found to be linear. The variation of electrical resistivity (ρ) with temperature (T) by heating the sample above RT has been determined. Resistivity is found to decrease with increase in temperature. Further the variation of electrical resistivity
(ρ) with temperature (T) from 77 K, liquid nitrogen temperature (LNT), to 270 K has also been determined. It is observed that resistivity suddenly
becomes zero at around 87 K. Thus the prepared material has superconducting properties with superconducting transition temperature,
T
c
at 87 K.
相似文献
13.
Ting LUO Yi ZHANG Xing-guo LI Li LIN Yue-yang ZHANG Qing-rong FENG 《Frontiers of Physics in China》2008,3(1):55-60
Systematic studies of synthesizing behaviors of sol-gel YBa2Cu3O7−x
samples in flowing oxygen atmosphere and their superconductivity have been performed. A set of high temperature ρ-T curves has been obtained for the whole synthesizing process. After four rounds of synthesizing, the resistivity of the sample
was around ρ=1.00×10−3Ω · cm at room temperature. The ρ-T curve of the fourth round shows that the orthorhombic to tetragonal phase transformation of the sample occurs around 600
°C, which is lower than that of the YBa2Cu3O7−x
sample prepared by conventional solid-state reaction method. Other measurements, such as X-ray diffraction, SEM measurement
and low temperature R-T and M-T measurement, were also performed. And the R-T and M-T measurement results suggest that during the synthesizing process, there exist some state at which the sample has better superconductivity
than the other states. Moreover, we found screw dislocations presenting on the sample broken surface from the SEM images.
This will change the concept that the screw dislocations can only grow on the surface of the YBCO thin films and single crystals.
相似文献
14.
K. I. Gnanasekar M. Sharon R. Pinto A. S. Tamhane S. C. Purandare S. P. Pai L. C. Gupta R. Vijayaraghavan 《Zeitschrift für Physik B Condensed Matter》1995,99(1):173-177
Structural and superconducting properties of the system Lu1−x
Ca
x
Ba2 Cu3O7−δ, both in bulk as well as thin film form, have been investigated. Presence of large Ca-ions at the Lu-sites is responsible
for phase stability (in 1–2–3 phase) in bulk. In argon annealed tetragonal samples (δ:1) superconductivity is reinstated as
in these samples, presence of Ca-ions lead to the generation of holes in the Cu−O planes. In oxygen annealed bulk samples
and thin films, there is a large depression ofT
c due to divalent Ca-ions present in concentrationx<0.2. Our data indicate that this depression ofT
c is likely due to overdoping effect. 相似文献
15.
TG/DAT evidence to support incorporation of fluorine into superconducting orthorhombic lattice in YBa2Cu3O6⋅+δ is presented. It is inferred that the F atom goes substitutionally in place of O atom in the lattice. Replacement of two
oxygen atoms by four fluorine atoms did not alter theT
cof the product. By a similar replacement of two of its oxygens by fluorine atoms, the tetragonal modification of the oxide
yields a product that remains non-superconducting down to 30 K. 相似文献
16.
Electronic plus phonon-exchange mechanism for high-temperature superconductivity in layered crystals
Sudhanshu S Jha 《Pramana》1987,29(6):L615-L625
A general mathematical formulation is developed for calculating the effective electron-electron interaction in layered crystals
like YBa2Cu3O7−δ, and for finding the resulting superconducting transition temperatureT
c in such systems within the framework of the conventional BCS pairing arising from various possible excitations in the medium.
This differs considerably from the usual case of an effective three-dimensional homogeneous system, and should be relevant
in the calculation ofT
c for the new class of high-T
c perovskites in which oxygen deficiencies in Cu-O layers and their distribution in the crystal play a crucial role. The explicit
form of the effective interactionV
jj(q
t,ω) in a given layerj in the unit cell of the crystal is found to be determined not only by the true polarization functionπ
j(q
t,ω) of that layer, but also of other layers. The exchange of electronic excitations of a nearby insulating layer by carriers
in a conducting layer thus becomes possible to get highT
c, with or without the usual phonon exchange. 相似文献
17.
A. Kondrat J. E. Hamann-Borrero N. Leps M. Kosmala O. Schumann A. K?hler J. Werner G. Behr M. Braden R. Klingeler B. Büchner C. Hess 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(4):461-468
We have prepared the newly discovered Fe-based superconducting material LaO1-xFxFeAs (0 ≤ x ≤ 0.2) in polycrystalline form and have investigated the samples by means of structural, thermodynamic and transport
measurements. Our investigations reveal a non superconducting phase at 0 ≤ x 0.04 which for x = 0 is characterized by a structural transition towards an orthorhombic distortion at Ts ≈ 160 K and antiferromagnetic spin order at TN ≈ 138 K. Both transitions lead to strong anomalies in various transport properties as well as in magnetization and in specific
heat. Remarkably, the transition temperatures are only weakly doping dependent up to x ≈ 0.04. However, the transitions are
abruptly suppressed at x ≥ 0.05 in favour of a superconducting phase with a critical temperature Tc
20 K. Upon further increasing the F-doping Tc increases up to a maximum of Tc = 26.8 K at x = 0.1 which is followed by a decrease down to Tc ≈ 10 K at x ≥ 0.15. 相似文献
18.
Li Fen Guo Tao Zhang Kai-cheng Chen Chin-ping Feng Qing-rong 《Frontiers of Physics in China》2006,1(4):446-448
Thick MgB2 (magnesium diborate) films, ∼10 μm, with T
c (onset) = 39.4 K and T
c (zero) = 39.2 K have been successfully grown on a stainless steel substrate using a technique called hybrid physical-chemical
deposition (HPCVD). The deposition rate is high, ∼6.7 nm/s. The X-ray diffraction (XRD) indicates that it is highly (101)
and c-axis oriented. The scanning electron microscope (SEM) images demonstrate that the film grown is in “island-mode”. The uniform
superconducting phase in the film is shown by the M-T measurement. 相似文献
19.
We report the results of Monte Carlo simulation of the phase diagram and oxygen ordering in YBa2Cu3O6+x
for low intra-sublattice repulsion. At low temperatures, apart from tetragonal (T), orthorhombic (OI) and ‘double cell’ ortho II phases, there is evidence for two additional orthorhombic phases labelled here asOI andOIII. At high temperatures, there was no evidence for the decomposition of theOI phase into theT andOI phases. We find qualitative agreement with experimental observations and cluster-variation method results. 相似文献
20.
D. R. Mishra 《Pramana》2008,70(3):535-541
The effects of gadolinium doping at calcium site on the normal and superconducting properties of Bi-2223 system were studied.
The Gd-doped (BiPb)-2223 series of specimens, namely Batch I, II and III were sintered at three different sintering temperatures
830, 850 and 895°C respectively. The properties investigated are (1) the normal state resistivity with a view to study metal-to-insulator
transition, (2) the XRD patterns of the specimens with a view to study the relative composition of (BiPb)-2212 and (BiPb)-2223
phases and (3) the superconducting fluctuation behaviour (SFB) with a view to determine the effect of doping, if any, on the
dimensionality of the fluctuation conductivity of the system. The normal state resistivity of Gd-substituted Bi-2223 specimens
shows metallic, semiconducting and insulating behaviour. The T
c
(R = 0) values indicate that (BiPb)-2223 phase is responsible for the observed superconducting transitions in Batch I and Batch
II specimens with Gd concentrations x ≤ 0.7. This observation is further confirmed in the analysis of XRD patterns of these specimens. Gadolinium, being a magnetic
impurity, has pair breaking effect near the Fermi level and decreases T
c
(R = 0). The analysis of the superconducting fluctuation behaviour (SFB) shows a 2D dimensionality without any cross-over.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献