ULTRASONIC EVALUATION OF OXYGEN-CONTENT, MODULUS, AND MICROSTRUCTURE CHANGES IN YBA2CU3O7-X OCCURRING DURING OXIDATION AND REDUCTION

Ultrasonic velocity measurements were used to evaluate the effects of oxidation and reduction on the oxygen content, elastic properties, and global microstructure of the YBa2Cu3O7-x ceramic superconductor for samples ranging from 70% to 90% of theoretical density. Bulk density, velocity, and Young's modulus generally increased with increasing oxygen content upon oxidation, and this behavior was reversible. Velocity image patterns obtained from ultrasonic scans were similar after oxidation and reduction treatments for a 90% dense sample, although the velocity value at any given point on the sample was changed following the treatments. The unchanging pattern correlated with destructive measurements showing that the spatial pore distribution (fraction and size) was not measurably altered after the treatments. Changes in superconducting behavior, crystal structure, and grain structure were observed consistent with changes in oxygen content.