This review article focuses on the sol-gel preparation of high temperature superconducting oxides wherein different classes of gel technologies were utilized. These involve: 1) the sol-gel route based upon hydrolysis-condensation of metal-alkoxides, 2) the gelation route based upon concentration of aqueous solutions involving metal-chelates, often called as “chelate gel” or “amorphous chelate” route, and 3) the organic polymeric gel route. This paper reviews the current status of these sol-gel processes, and illustrates the underlying chemistry involved in each sol-gel technology. It is demonstrated that the chemical homogeneity of the gel is often disturbed by the differences in the chemistries of the cations. Prior to gelation the starting precursor solution containing various forms of metal-complexes must be chemically modified to overcome this problem. Illustration of a variety of strategies for success in obtaining a homogeneous multicomponent gel with no precipitation is focal point of this review article.

Invited review “sol-gel” preparation of high temperature superconducting oxides

The polyacrylamide gel: A novel route to ceramic and glassy oxide powders

http://eprints.nmlindia.org/539/1/2002(2).pdf

Effect of pH on the combustion synthesis of nano-crystalline alumina powder

The preparation of Y?Ba?Cu-oxide (YBCO) powder by various techniques is critically reviewed and the synthesis of ultrafine superconducting YBa2Cu3Ox(123) powders is specially emphasized. The fine powder has assumed a large importance, requiring the minimization of processing parameters (time and temperature) during calcination, homogenization and sintering to avoid the problems of evaporation of the constituent oxides. From the voluminous research activities on YBCO it is known that by adopting any preparation technique the superconducting transition temperature (Tc) value of ?92?K could be achieved in the bulk samples, thus in this review the Tc values are not emphasized. Also, the other transport properties such as critical current densities (Jc) and magnetic properties are not discussed, since these properties are mainly controlled by many other parameters related to the weak link across the grain boundaries of the specimens, and a very little role is played by the synthetic procedure. The weak links across the grain boundaries are known to be the cause for the poor Jc values in bulk specimens and those weak links are observed due to the presence of impurities at the grain boundaries, misorientation of grains and oxygenation of the samples. By selecting the proper synthetic procedure, only the impurity problem can be solved, and to remove the other problems, a proper fabrication method needs to be adopted. This review will guide the new researcher to find the appropriate technique to synthesize good quality YBCO powder.

https://iopscience.iop.org/article/10.1088/0953-2048/18/9/R01/pdf

A review on the synthesis of Y?Ba?Cu-oxide powder

Steady‐state flow stress of dense (99% of theoretical) polycrystalline YBa2Cu3O7−δ has been measured in direct compression at temperatures between 870 and 980 °C in oxygen partial pressures of 0.03, 0.18, and 1.0×105 Pa for strain rates between 5×10−6 and 4×10−5 s−1. The stress exponent was close to one, indicating that diffusional flow was the dominant deformation mechanism. The flow stress decreased with decreasing oxygen partial pressure, obeying a power law with an exponent of approximately 1/2 . The activation energy was about 800 kJ/mol at an oxygen partial pressure 1×105 Pa, but decreased to 600 kJ/mol at a pressure of 3×103 Pa.

High‐temperature deformation of YBa2Cu3O7−δ

The high-Tc superconducting oxide Yba2Cu3O7–y has been prepared by the amorphous citrate process. A citrate-nitrate solution was prepared at room temperature and dehydrated at around 80°C to yield a solid precursor material. The precursor was fired to high temperature to form the desired compound. The decomposition mechanism was studied with thermogravimetric analysis and X-ray diffraction. Intermediate products were formed during the decomposition reactions. Nearly phase-pure Yba2Cu3O7-y powders were obtained by firing the precursor in air to 900°Cfor2 h. Sintered samples were typically over 90% dense and exhibited good superconducting properties.

Preparation of High-Tc Superconducting Oxides by the Amorphous Citrate Process

The knowledge of the steady-state stress for plastic deformation as a function of temperature and strain rate is essential for hot-forming superconducting material into commercially useful shapes. In this paper, results are presented on the experimental determination of the rheology of fully dense polycrystalline Y1Ba2Cu3O7−x superconducting material at temperatures ranging from 750° to 950°C and strain rates of 10−4, 10−5, and 10−6 s−1. The data are best fitted by a power law: e(s−1)=8.9 × 10−17. (s−1) σ2.5 (Pa) exp [−2.01 × 105(J·mol−1)|RT]. X-ray analysis shows that the superconducting material retains its phase composition after nearly 70% total strain of the sample. A strong anisotropy in the resistivity of the deformed samples is observed because of the development of a preferred orientation of the a or b axis of Y1Ba2Cu3O7−x orthorhombic perovskite single crystals perpendicular to the principal maximum compressive stress.

Effects of Temperature and Strain Rate on the Plastic Deformation of Fully Dense Polycrystalline Y1Ba2Cu3O7−x Superconductor

Effects of Temperature and Strain Rate on the Plastic Deformation of Fully Dense Polycrystalline YBa2Cu3O7-x Superconductor.

Preparation de YBa 2 Cu 3 O 7−x densifie par forgeage a chaud sous une haute pression de confinement. Developpement d'une orientation de grain preferentielle dans les poudres frittees par deformation plastique sous haute temperature et haute pression. Determination du comportement rheologique de YBa 2 Cu 3 O 7−x prefritte

Chung-tse Chu

Papers

Preparation of High-Tc Superconducting Oxides by the Amorphous Citrate Process

Effects of Temperature and Strain Rate on the Plastic Deformation of Fully Dense Polycrystalline Y1Ba2Cu3O7−x Superconductor

Effects of Temperature and Strain Rate on the Plastic Deformation of Fully Dense Polycrystalline YBa2Cu3O7-x Superconductor.

Effects of temperature and strain rate on the plastic deformation of fully dense polycrystalline Y1Ba2Cu3O7−x superconductor

Preparation of High-Tc Superconducting Oxides by the Amorphous Citrate Process.