Citrate Pyrolysis Method Research Articles

Study of the Properties of YBCO Superconductor Compound in Various Preparation Methods: A Short Review

Superconductors have entered into many applications and advanced technological fields, due to their excellent properties identified by zero resistance and expelling the magnetic field applied to them. Superconductivity is a viable technology to prevent energy losses contributed by electrical resistivity. Also, the magnetic flux is repelled entirely out of the body of superconducting material which makes the Meissner Effect. High-Temperature Superconductors (HTS) have become the focus of researchers and scientists. This is because it uses liquid nitrogen "LN" in cooling, which gives it significant critical temperatures compared to traditional materials based on liquid helium "LHe" in cooling. From this point of view, began to employ these materials in most disciplines and modern technologies. In this article, the phenomenon of Superconductivity will define with explain its most prominent characteristics and focus on the preparation of the HTS (Yttrium-Barium-Copper-Oxide) compound (Abbreviated as YBCO) in different methods "The Sol-Gel and Citrate Pyrolysis Methods", to creating ultrafine superconducting (Y-123) powders. Generally known that by adopting any preparation technique, the superconducting transition temperature (Tc) value of ≈ 92 K could be achieved in the bulk samples. The Citrate Pyrolysis method is a unique route to prepare reactive precursor mixtures through an ignition process of a concentrated aqueous solution including metallic ions of stoichiometric composition. This procedure enables to synthesize of highly homogeneous and fine powders for functional materials, in comparison to the Sol-gel technique.

Structural, physical and photocatalytic properties of mixed-valence double-perovskite Ba2Pr(Bi,Sb)O6 semiconductor synthesized by citrate pyrolysis technique

We demonstrated crystal structures, magnetic, optical, and photocatalytic properties of the B-site substituted double perovskite Ba2Pr(Bi1–xSbx)O6 (x = 0, 0.1, 0.2, 0.5 and 1.0) synthesized by the citrate pyrolysis method. The single-phase polycrystalline samples with the light Sb substitution crystallized in a monoclinic structure (I2/m). Magnetization measurements on all the samples showed that the effective magnetic moments are concentrated around 3 μB, indicating the valence mixing states between Pr3+ and Pr4+. The magnitudes of band gap energy for the two end member samples were estimated from the optical measurements to be Eg = 1.06 eV at x = 0 and 2.71 eV at x = 1.0. The Ba2Pr(Bi1–xSbx)O6 (x = 0, and 0.1) powders obtained by the present technique exhibited enhanced photocatalytic activities when compared to the same compounds prepared by the conventional solid state method. Our findings suggest that the higher photocatalytic activities strongly depend on powder preparation methods as well as the band gaps and photogenerated charge separation.

Superconductivity and structural characteristics of ceramic Pr2Ba4Cu7O15−δ prepared by ambient pressure synthesis using citrate pyrolysis method

Sintered material of Pr2Ba4Cu7O15−δ (Pr247) was synthesized at ambient pressure condition by using citrate pyrolysis precursor method, and the superconductivity caused by oxygen reduction treatment has been confirmingly observed and examined.By resistivity and magnetization experiments, it has been found that the critical temperature Tc of the reduced samples could reach about 10K higher than previously reported data for pure Pr247. Besides, from TEM observations, the present material was found to be heterogeneous system containing Pr247, Pr124 and novel stacking structure phases rich in CuO single chains. These results have suggested that oxygen–reduction at such region rich in the CuO single chains may affect the superconductivity of the adjacent crystal region containing CuO double chains, and might enhance the superconductive critical temperature.

Electrical conductivity and gas sensitivity to VOCs of V-doped ZnFe2O4 nanoparticles

ZnFe2O4 and V-doped ZnFe2O4 nanoparticles were successfully fabricated by citrate pyrolysis method. The structural and morphological characteristics of the as-sintered powders were investigated by means of XRD and FE-SEM. The results showed all the as-received powders have a spinel-type structure, irrespective of the added V content, and the average size of the spherical particles is below 50 nm with good dispersity. The resistance of ZnFe2O4-based thick films decreases with increasing the added V content. It is found that the added V has different effects on the sensitivities to different VOCs. Due to the added V, the sensitivities to ethanol and acetone decline greatly and the highest sensitivity temperatures increase, whereas the added V enhances remarkably the sensitivities to benzene, toluene and xylene at high operating temperature. The V-doped ZnFe2O4 can be promising as a sensing material for gas sensor detecting benzene and its derivatives.

Structural and magnetic characterization of super fine grain ceramics of YBa 2Cu 4O 8 synthesized by citrate pyrolysis method

YBa 2Cu 4O 8 (124) is synthesized at ambient pressure condition using citrate pyrolysis precursor method, and the weakly sintered 124 ceramics are studied by both SEM observation and ac magnetization measurement. Such ceramics can be regarded as a system of weak-coupled super fine grains, so that we may study experimentally the intergrain superconductive phase transition considering the effects of mesoscopic sintered structure. For this purpose, several specimens at different treatment time stage in the sintering process are examined. As the sintering is advanced, very small grains are fused into larger ones and the adjacent large grains tend to be fused at their interface. From magnetic measurements, the ceramics are equally confirmed to be weak-coupled grain systems which show the intergrain ordering at each T c2 determined consistently by sintering temperature. Utilizing the series of ceramics, we will be able to study the intergrain ordering further systematically.

Synthesis of YBa 2Cu 4O 8 under one bar oxygen pressure by the citrate pyrolysis method

The citrate pyrolysis method is used to investigate the synthesis process and the superconducting transitions of the YBa 2Cu 4O 8 (124) phase. DC susceptibility measurements show that the intrinsic Tc, both for the one bar sintering route and the 90 bar treatment, is close to 82 K. In the former case, however, the reaction temperature must not exceed 800°C, and χ ec and resistive transitions are severely degraded due to the extremely small grain size.

Superconducting properties of Y 1−xPr xBa 2Cu 4O 8 prepared by the citrate pyrolysis method

Superconducting properties are examined in Y 1−xPr xBa 2Cu 4O 8 synthesized by the citrate pyrolysis method followed by sintering in a one atm oxygen flow. Lattice constants increase linearly, while the orthorhombicity decreases linearly with increasing x. Meissner effect measurements indicate that the onset T c decrease monotonically with the Pr substitution, and disappears at x=0.75. This is caused by the change in the hole concentration with the substitution of Pr for Y.

Specific-heat, resistivity and magnetization study on polycrystalline YBa2Cu4O8

Abstract Specific-heat measurements around the critical temperature on poly-crystalline YBa2Cu4O8 prepared by the citrate-pyrolysis method show a distinct anomaly ΔC/Tc≈15 mJ/(mol K2) at Tcalor.c ≈ 88 K. This transition temperature is almost 10% higher than reported in previous studied and is supposed to be due to a carrier concentration slightly different from samples prepared by the conventional high-pressure synthesis. The magnetization and transport data are compared with data from the literature and interpreted assuming two independent energy bands in YBa2Cu4O8.

Diamagnetic properties of YBa 2Cu 3O 7−δ presintered powders: Critical current densities and a.c. losses

The intrinsic diamagnetic response of YBa 2Cu 3O 7−δ presintered powders obtained by the citrate pyrolysis method has been studied. The techniques applied were: a.c. susceptibility at zero d.c. field, low field d.c. susceptibility, isothermal magnetization and a.c. susceptibility at varying bias fields up to 5 T. To investigate intragrain links, powders of known sizes were used directly, dispersed in oil and finally in the sintered form. Intragrain inductive critical currents and critical field values are derived. Finally, the experimental results are discussed within the framework of weak link models and flux pinning effects.

Improvements of sintered YBCO samples by citrate pyrolysis and ozone annealing

YBCO sintered samples have been fabricated by the citrate pyrolysis method. The annealing, with the usual thermal processes, but using a mixture of oxygen and ozone, generates large microcrystals. Samples fabricated with this process have been characterized by measuring the a.c. susceptibility. Low field measures show a very narrow transition width, while high field measures performed both at 50 and 100 Gauss denote the higher strength of the intergranular junctions in the ozone made samples.

Specific heat, magnetic susceptibility and superconductivity of YBa2Cu3O7−δ doped with iron

Abstract YBa 2 (Cu 1- x Fe x ) 3 O 7- δ with x =0, 1%, 2% and 4% was prepared by the citrate pyrolysis method. The samples were characterized by X-ray diffraction, micrographs, electron microprobe, a.c. susceptibility near the critical temperature T c , field cooling Meissner effect, d.c. susceptibility from 100 to 250 K and specific heat from 1 to 300 K. These measurements confirm that iron does not segregate. The localized moment is close to 4.0 μ B /Fe-atom and the constant component of the susceptibility increases from 283 to 530 x 10 -6 /mol-f.u. Calorimetric data indicate that for x ⩾2% the superconducting phase is no longer homogeneous. The low-temperature linear term in the specific heat reflects a growing non-superconducting fraction. The apparent contradiction between a high Meissner effect at 4 K and the absence of any definite specific heat jump at T c in the sample with x =4% is understood as an effect of the short coherence length in the presence of repulsive defects. Using the latter tetragonal sample as a normal reference compound, the shape of the specific heat difference C s - C n near T c for the undoped sample ( calorimetric transition width: 1.3 K, δC / T c =49 mJ /( K 2 mol )) is discussed.