Abstract
Using fine powders of YBa2Cu3Oy superconducting oxides of which particle size are about 3μm in average diameter, relations between the reaction mechanisms for oxidation and reduction, and the change in their crystal structures, which occurred within each particle, have been investigated. In a case of isothermal reduction using orthorhombic powders(oxygen content y is 6.92), it was made clear that the reaction was controlled by the removing rate of oxygen from the particle surface, so that there existed a uniform concentration of oxygen in a particle. On the other hand, in a case of isothermal oxidation of tetragonal powders(y=6.00), the reaction was recognized to be controlled by the moving rate of interface between tetragonal and orthorhombic phases, and accordingly the co-existence of two phases was confirmed by X-ray diffraction. The authors tried to analyze this oxidation-process using "Unreacted Core Model", and the activation energy of 51.3 kJ/mol was obtained. Similar experiment of isothermal oxidation was carried out upon the orthorhombic powders(y=6.44). Brief discussion was made for the experimental results obtained.
