Superconductivity at 40K in Cesium Doped C60

1994 ◽  
Vol 359 ◽  
Author(s):  
T.T.M. Palstra ◽  
O. Zhou ◽  
Y. Iwasa ◽  
P.E. Sulewski ◽  
R.M. Fleming ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Charge Transfer ◽  
Transition Temperature ◽  
Liquid Ammonia ◽  
Ac Susceptibility ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Two Phases ◽  
Fcc Structure

ABSTRACTWe report superconductivity in Cs3 C60 at 40K using ac susceptibility measurements under hydrostatic conditions up to 15 kbar. Cs3 C60 was prepared by reaction of C60 with Cs in liquid ammonia, followed by heating at 150°C. This route circumvents formation of the energetically more stable CSl C60 and Cs4 C60 phases. We have studied the synthesis and phase formation by measuring the symmetric Ag pentagonal pinch mode of C60 using Raman spectroscopy. Whereas Raman spectroscopy indicates homogeneous charge transfer of three electrons, x-ray diffraction indicates two phases other than the commonly observed fcc structure. This superconducting transition temperature is considerably higher than for known doped C60 compounds and intermetallic compounds.

COMPOSITION DEPENDENCE OF SUPERCONDUCTIVITY AND CRYSTAL STRUCTURE IN La(Ba1−xCax)2Cu3O7−y SYSTEM

1989 ◽  
Vol 03 (04) ◽  
pp. 307-311 ◽  
Author(s):  
N. CAO ◽  
J.Q. ZHENG ◽  
X.Y. SHAO ◽  
X.S. CHEN ◽  
W.Y. GUAN
Keyword(s):  
Crystal Structure ◽  
Transition Temperature ◽  
Superconducting Transition Temperature ◽  
Composition Dependence ◽  
Superconducting Transition ◽  
Orthorhombic Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Resistivity Measurements ◽  
Zero Resistance

The composition dependence of superconductivity and crystal structure in La ( Ba 1−x Ca x)2 Cu 3 O 7−y system was determined by the resistivity measurements and X-ray diffraction analysis. The superconducting transition temperature is raised with the increase of Ca content till x=0.6, at which the zero resistance temperature of the sample is 81.5 K. In the meanwhile, the crystal structure of the sample changed from tetragonal (x=0) to orthorhombic structure (x=0.2, 0.4, 0.6). With further increase of Ca content, the superconductivity decrease for the sample of x=0.8 with mixed phases including the orthorhombic oxygen-deficient perovskite-like (ODP) structure and no superconducting transition is found at 4.2 K for the sample of x=1 without the ODP structure. A possible explanation of these experimental results is given.

Crystallographic studies on single crystals of doped and undoped Bi-Sr-Ca-Cu-O superconductors

1990 ◽  
Vol 48 (4) ◽  
pp. 78-79
Author(s):  
Brigitte H. Krause ◽  
Y. C. Chang ◽  
P. Z. Jiang ◽  
D. J. Lam
Keyword(s):  
Transition Temperature ◽  
Single Crystals ◽  
Layer Structure ◽  
The Other ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Layer Sequence ◽  
Tetragonal Unit Cell ◽  
Chemical Disorder

Diffraction data on single crystals of low Tc phase of Bi-Sr-Ca-Cu-O superconductor indicated a well developed layer structure, but with structural and chemical disorder within the layers. The lattice constant c and the layer sequence for the pseudo-tetragonal unit cell were determined from x-ray diffraction measurements of the 006 reflections. They were found to be 30.84(2) Å for the undoped compound and the same 30.84(2) Å for the lead doped crystals indicating the low superconducting transition temperature (Tc = 80 K) phase. The c-dimension for single crystals doped with both antimony and lead was 29.02(5) Å. Polycrystalline samples of that compound on the other hand formed the high temperature (Tc = 107 K) modification with c = 36.9(6) Å, determined from electron diffraction. A mixture of phases with different stacking of layers was indicated by splitting of diffraction spots. The direction of c was also less well defined in the lead-antimony doped single crystals than in the other two compounds.

Oxygen Stoichiometry and Superconductivity in Ho1Ba2Cu3O7−x

1987 ◽  
Vol 99 ◽  
Author(s):  
B. C. Sales ◽  
Y. C. Kim ◽  
J. R. Thompson ◽  
D. K. Christen ◽  
L. A. Boatner ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Transition Temperature ◽  
High Resolution ◽  
Oxygen Vacancies ◽  
Oxygen Stoichiometry ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
General Shape ◽  
X Ray ◽  
Lattice Constants

ABSTRACTThe effects of varying oxygen content on the superconducting transition temperature Tc, resistivity, and crystal structure of HoBa2Cu3O7−x (0 < x < 1) have been investigated. The variation of Tc wltn 8 is very similar to that previously reported by several authors for YBa2Cu3O7−x [1,2]. In particular a plateau in the Tc vs x curve is observed for values of x between 0.3 and 0.4 witfi the value of Tc,(10 % onset measured magnetically) remaining relatively constant at about 55 K. The width of the superconducting transition, as measured both resistively and magnetically, is substantially narrower for x= 0.35 + 0.05 than for slightly larger or smaller values of x. High resolution powder x-ray diffraction analysis was used to measure the lattice constants of both the orthorhombic and tetragonal phases as x was varied. With increasing x the temperature coefficient of the resistivity changed from positive (metallic) for x ≤0.2 to negative (semiconducting) for x ≥, 0.3. Since the general shape of the Tc vs x curve was unaffected by the complete substitution of magnetic Ho for Y, these results suggest an ordering of the oxygen vacancies in the a-b plane and the existence of an ordered compound with a Tc of 55 K.

scholarly journals Role of the extra Fe in K2−xFe4+ySe5 superconductors

2019 ◽  
Vol 116 (4) ◽  
pp. 1104-1109 ◽  
Author(s):  
Chih-Han Wang ◽  
Chih-Chien Lee ◽  
Gwo-Tzong Huang ◽  
Jie-Yu Yang ◽  
Ming-Jye Wang ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Parent Compound ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Heat Treated ◽  
Different Temperatures ◽  
Two Phases ◽  
Best Fit

The exact superconducting phase of K2−xFe4+ySe5 has so far not been conclusively decided since its discovery due to its intrinsic multiphase in early material. In an attempt to resolve this mystery, we have carried out systematic structural studies on a set of well-controlled samples with exact chemical stoichiometry K2−xFe4+xSe5 (x = 0–0.3) that are heat-treated at different temperatures. Using high-resolution synchrotron radiation X-ray diffraction, our investigations have determined the superconducting transition by focusing on the detailed temperature evolution of the crystalline phases. Our results show that superconductivity appears only in those samples that have been treated at high-enough temperature and then quenched to room temperature. The volume fraction of superconducting transition strongly depends on the annealing temperature used. The most striking result is the observation of a clear contrast in crystalline phase between the nonsuperconducting parent compound K2Fe4Se5 and the superconducting K2−xFe4+ySe5 samples. The X-ray diffraction patterned can be well indexed to the phase with I4/m symmetry in all temperatures investigated. However, we need two phases with similar I4/m symmetry but different parameters to best fit the data at a temperature below the Fe vacancy order temperature. The results strongly suggest that superconductivity in K2−xFe4+ySe5 critically depends on the occupation of Fe atoms on the originally empty 4d site.

SEM and XRD Characterization of Ni-Hf Alloys at Low Hf Concentration

2006 ◽  
Vol 518 ◽  
pp. 325-330 ◽  
Author(s):  
Ana Umićević ◽  
H.E. Mahnke ◽  
Bozidar Cekić ◽  
Jasna Grbović Novaković ◽  
V. Koteski ◽  
...  
Keyword(s):  
Local Structure ◽  
X Ray Diffraction ◽  
Characterization Methods ◽  
X Ray ◽  
Additional Information ◽  
The Third ◽  
Two Phases ◽  
X Ray Absorption ◽  
Fcc Structure

The alloying and phase formation in Ni-Hf samples with 0.2-, 2-, and 5-at.% Hf were studied by X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). Both characterization methods, XRD and SEM, reveal the presence of the HfNi5 phase (fcc structure) where the excess Ni atoms are present in the form of Ni or Ni-rich segregations in the sample containing 5-at.% Hf. The sample with 2-at.% Hf is characterized by the presence of the two phases present in the 5-at.% sample and by Hf atoms, which occupy substitutional lattice positions in the Ni lattice. Finally, in the third sample with 0.2-at.% Hf, the Hf atoms mainly substitute the Ni atoms in the lattice. This analysis is being complemented with additional information on the local structure around Hf by extended X-ray absorption fine structure spectroscopy (EXAFS).

CHARACTERIZATION OF POTASSIUM DOPED GdBa2Cu3O7−δ USING RAMAN SPECTROSCOPY AND X-RAY DIFFRACTION

1995 ◽  
Vol 09 (26n27) ◽  
pp. 1739-1752
Author(s):  
PREETHI CICILY THOMAS ◽  
MANOJ KUMAR K. ◽  
V. UNNIKRISHNAN NAYAR ◽  
VIDYALAL V. ◽  
C.P.G. VALLABHAN
Keyword(s):  
Raman Spectroscopy ◽  
Raman Spectra ◽  
Tetragonal Phase ◽  
Orthorhombic Phase ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Resistivity Measurements ◽  
Xrd Patterns

Potassium doped and undoped GdBa 2 Cu 3 O 7−δ have been prepared and superconducting transition temperatures between 92 K and 100 K have been determined from resistivity measurements. Raman spectra of doped and undoped samples are identical and they contain bands corresponding to both the superconducting orthorhombic phase and nonsuperconducting tetragonal phase. XRD patterns also reveal both the phases. Raman spectra recorded at 92 K of undoped GdBa 2 Cu 3 O 7−δ and doped GdBa 2 Cu 3 O 7−δ with weight percentages 0.75, 1.00, 1.25 and 1.50 of K shows a softening of the band at 338 cm−1.

Superconducting YBa2Cu3O7−x fibers from the thermoplastic gel method

1989 ◽  
Vol 4 (4) ◽  
pp. 787-794 ◽  
Author(s):  
Fusaoki Uchikawa ◽  
John D. Mackenzie
Keyword(s):  
Transition Temperature ◽  
Surface Area ◽  
Superconducting Transition Temperature ◽  
Organic Content ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
Shrinkage Ratio ◽  
X Ray ◽  
Zero Resistance ◽  
Solution Route

The successful fabrication of ceramic superconducting YBa2Cu3O7−x fibers has been investigated. A new method was proposed for synthesis of the fibers through a solution route. The thermoplastic gels were synthesized using Y, Ba, Cu, ethoxides, and diethylenetriamine. The fibers were drawn from the reheated gels. The fibers were characterized by x-ray diffraction, SEM, and shrinkage ratio measurements. The fired and then annealed fiber is shown to have a superconducting transition temperature of 91 K (onset) and zero resistance temperature of 84 K. With regard to the fired fibers, it is found that the surface area increased and superconducting transition temperature decreased with increasing organic content in the initial gel. The usefulness of this method is shown and the structure of the synthesized gel is discussed.

scholarly journals Effect of sintering time on Bi1.6Pb0.4Sr1.8Ba0.2Ca2Cu3O10+? compound quenched in air and liquid nitrogen

2014 ◽  
Vol 11 (2) ◽  
pp. 713-717
Author(s):  
Baghdad Science Journal
Keyword(s):  
Liquid Nitrogen ◽  
Solid State Reaction Method ◽  
Nominal Composition ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
High Tc ◽  
X Ray ◽  
Sintering Time ◽  
High Tc Phase ◽  
Two Phases

High temperature superconductor with nominal composition Bi1.6Pb0.4Sr1.8Ba0.2Ca2 Cu3O10+? was prepared by solid state reaction method. Two sets of samples have been prepared .The first one was quenched in air; the second set was quenched in liquid nitrogen. X-ray diffraction analyses showed an orthorhombic structure with two phases, high –Tc phase (2223) and low-Tc phase (2212) in addition to that impure phase was found. It has been observed that quenched in air samples display a sharp superconducting transition and a higher-Tc phase than that of the quenched in liquid nitrogen samples.

Superconducting and Magnetic Properties of (Ru1-xNbx)Sr2(Eu1.5Ce0.5)Cu2Oz

2003 ◽  
Vol 17 (18n20) ◽  
pp. 3682-3687 ◽  
Author(s):  
H. K. Lee ◽  
Y. C. Kim
Keyword(s):  
Magnetic Properties ◽  
Magnetic Susceptibility ◽  
Transition Temperature ◽  
Meissner Effect ◽  
Internal Field ◽  
Electric Transport ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Vortex Phase

The ( Ru 1-x Nb x) Sr 2( Eu 1.5 Ce 0.5) Cu 2 O z(0 ≤ x ≤ 0.5) compounds have been synthesized and characterized by X-ray diffraction, electric transport, and magnetic susceptibility measurements. We find that there is no significant change in the superconducting transition temperature when Nb is substituted for Ru up to x = 0.5. Unlike RuSr 2( Eu 1.5 Ce 0.5) Cu 2 O z, bulk Meissner effect is observed in the field-cooled magnetization measurements of the Nb doped samples. The experimental results are discussed in conjunction with a reduction of the internal field caused by the Nb substitution for Ru, based on the spontaneous vortex phase interpretation.

STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF Bi4Sr3Ca3CuyOw AND Bi4Sr3Ca3Cu4−xMxOz(M=Fe, Cr AND Mn) GLASS CERAMICS

1995 ◽  
Vol 09 (04n05) ◽  
pp. 549-561 ◽  
Author(s):  
E. ZACHARIAS ◽  
R. SINGH
Keyword(s):  
Dopant Concentration ◽  
Ac Susceptibility ◽  
Glass Ceramics ◽  
Lattice Parameter ◽  
Superconducting Transition ◽  
Superconducting Properties ◽  
X Ray Diffraction ◽  
Dopant Content ◽  
X Ray ◽  
Ceramic Superconductors

The synthesis of glass ceramic superconductors of Bi 4 Sr 3 Ca 3 Cu y O w(3≤y≤6) and Bi 4 Sr 3 Ca 3 Cu 4−x M x O z ( M=Fe , Cr , Mn and 0≤x≤0.2) compositions is reported. The 4334 sample is found to be the optimum composition to obtain Bi-2212 superconducting phase. X ray diffraction studies indicate that the solid solubility of 3d metal ions in the 4334 system is limited to x=0.05 in the case of Fe and Cr and x=0.1 in the case of Mn. A systematic decrease in Tc with increasing dopant concentration is observed from resistivity as well as AC susceptibility measurements. Tc depression rates, however, are found to differ for different dopants. XRD studies indicate the decrease in c lattice parameter with increase in dopant content. The systematics of the superconducting transition is discussed in view of Tc depression rates.

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