共查询到6条相似文献,搜索用时 15 毫秒
1.
S Rayaprol Krushna Mavani CM Thaker DS Rana Keka Chakravorty SK Paranjape M Ramanadham Nilesh A Kulkarni DG Kuberkar 《Pramana》2002,58(5-6):877-880
A new series of mixed oxide superconductors with the stoichiometric composition La2−x
Dy
x
Ca
y
Ba2Cu4+y
O
z
(x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La2−x
(Y/Er)
x
Ca
y
Ba2Cu4+y
O
z
series, show a strong dependence of T
c on hole concentration (p
sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant
displacement of La onto Ba site. Superconductivity studies show that maximum T
c is obtained for x=0.5, y=1.0 sample (T
c ∼ 75 K), for La1.5Dy0.5Ca1Ba2Cu5O
z
(La-2125). 相似文献
2.
In this paper the kinetics of oxygen desorption from Y Ba2Cu3O7-δ has been investigated and measurements carried out in the temperature range 350–750 C. It is shown that the oxygen desorption
is diffusion-controlled (and not surface-controlled), and characteristic of diffusion from small grains in a loosely coupled
porous matrix. At every temperature a number of time constants with well-defined ratios appear and have been identified and
measured. These time constants can be related to the average bulk diffusion constant which shows an Arrhenius behaviour with
deviations around 750°C which are ascribed to the well-known orthorhombic to tetragonal transition. In this paper we establish
the basic underlying physical mechanism of oxygen desorption in Y Ba2Cu3O7-δ. 相似文献
3.
Superconductivity is found in tetragonal La3−x
Ba3+x
Cu6O14+δ and La, Ba)6−x
Sr
x
Cu6O14+δ even though they do not possess Cu-O chains or the K2NiF4 structure. Resistivity measurements confirm the occurrence of a transformation from chain-superconductivity to sheet-superconductivity
in YBa2Cu3O7−δ as δ is varied in the range 0.0–0.5.
Contribution No. 481 from the Solid State and Structural Chemistry Unit 相似文献
4.
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
5.
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
6.
Mössbauer study of orthorhombic and tetragonal YBa2(Cu1-xFex)3O7-σ;x=0.02, 0.04, 0.08 has been done to investigate the two inequivalent Cu-sites. Fe substituting Cu having pyramidal oxygen co-ordination is in Fe3+ state while Fe substituting Cu having square planar co-ordination is in Fe3+ and Fe4+ states in dynamic equilibrium. 相似文献