Synthesis and characterization of YBa₂Cu_3-xSb_xO_7-δhigh-temperature superconductors

Abstract

The effects of Sb doping on YBa 2 Cu 3 O 7−δ high-temperature superconductors have been investigated. Samples were synthesized for the nominal compositions of YBa 2 Cu 3−x Sb x O 7−δ where x = 0.0-0.3 by solid-state preparative techniques. These materials were prepared under different conditions, such as heating in an air or an oxygen flow, followed by furnace cooling or quenching in air or in liquid nitrogen. These results show that for the air-quenched samples these materials are superconducting when 0.01 x 0.1, whereas for the furnace-cooled samples T c gradually decreases with increasing Sb concentration. However, in both cases zero resistance was not achieved down to 72 K when x 0.2.To understand the effects of Sb doping on the structure of YBa 2 Cu 3 O 7−δ x-ray absorption spectroscopy, x-ray diffraction and scanning electron microscopy have been applied. These results indicate that the valence state of copper is almost the same in the pure and the doped YBa 2 Cu 3−x Sb x O 7−δ . It has been observed that doping with low concentrations of Sb (x 0.1) and slow cooling have similar effects on the structure of YBa 2 Cu 3 O 7−δ , i.e. these help to stabilize the orthorhombic structure. Whereas, with higher concentrations of Sb (x 0.2), all compositions of liquid-nitrogen-quenched YBa 2 Cu 3−x Sb x O 7−δ and air-quenched pure YBa 2 Cu 3 O 7−δ stabilize in the tetragonal geometry. In superconducting materials the particles are smaller, uniformly distributed and the grains are linked together, whereas in non-superconducting materials the particles are larger and the grains are not well connected.

Cation distribution in nanocrystalline ZnFe2O4investigated using x-ray absorption fine structure spectroscopy

“…For each spectrum a theoretical model was achieved by adding shells around the central excited atom and least-squares iterating the Fermi energy (E 0 ), the radial distances (RD) and the Debye-Waller type factors (DWF). Although the coordination numbers (CN) can be iterated, due to their strong correlation with Debye-Waller type factors [28,29] in the present study coordination numbers were kept fixed to their preset values. The structural uncertainties for RD and CN are about ±0.02 Å and ±10%, respectively, for nearest neighbours, increasing slightly for distant shells.…”

Realistic dielectric response of high temperature sintered ZnO ceramic: a microscopic and spectroscopic approach

“…37,38 The observed DWFs of second shells are also higher compared to other shells but remain almost same for temperatures of 1300 C and 1400 C. High DWFs generally indicates a high degree of local disorder around the absorbing atoms and suggest introduction of atomic vacancies. 39 Present study suggests that high temperature sintering of ZnO at 1200 C introduces local disorder that remains unchanged on further sintering temperatures of 1300 C and 1400 C. In ZnO, oxygen vacancy (V O ) and zinc vacancy (V Zn ) are respectively considered to introduce shrinkage and expansion in the lattice parameters 40 and presence of V Zn is also reported in the second coordination shell. 41 Therefore, observed increase in the DWFs and radial distances of the second shell Zn-Zn atoms suggests introduction of local disorder around Zn absorbing atoms due to possible creation of V Zn .…”

Effect of Antimony (Sb) Substitution on Ba-Site of Porous Structured YBA2Cu3Oδ Superconductor

“…∆T of the samples varied with Sb concentration and the largest ∆T was observed at x = 0.30, which is 14 K. Below the optimum concentration of Sb x = 0.15, T C zero and T C onset were not showing obvious changes which indicate that low concentration of Sb has a moderate effect on the conduction mechanism and also acts as the oxygen stabilizer that maintains the orthorhombicity of the structure. At the high level of Sb doping, depression of T C maybe because of Ba disorder that might dominate over the oxygen intake which led to the disturbance of orthorhombic symmetry and hence suppresses the T C [6]. For sample x = 0.30 that exhibit the lower T C zero might be due to the decreasing of oxygen content x < 6.4, thus could be led to the expansion of c axis and become tetragonal structure.…”

“…020) and (116) are proof of 123 phases and were successfully indexed. Optimum splitting between the regions 31.5˚ ≤ 2θ ≤ 33.5˚ can be clearly observed indicates that it has orthorhombic structures because the region is related to the tetragonal-orthorhombic phase transformation [6]. If a sample exhibit tetragonal structure, the peaks are merged together and the splitting cannot be seen.…”

“…The best sample contains 60 vol % of the pores with a T C of 91 K and has a small superconducting transition of 2-3 K. It was reported that porous YBCO is more susceptible to magnetic field because the magnetic field in the structure did not have to be removed out from the sample, while in high dense YBCO the magnetic field was pushed out during the superconducting transition [5]. Doping of Sb to the Cu sites in YBCO superconducting system YBa 2 Cu 3-x Sb x O 7-δ by furnace cooling method was carried out [6]. T C zero decreased gradually with increasing of Sb content and when x = 0.3, zero resistance was not achieved anymore.…”