Eddy Current Sensing of Oxygen Content in High-T_c Superconductors

Abstract

The superconducting properties of Ba₂YCu₃O_7-x are strongly dependent on the amount of oxygen contained in the material. Although the physical mechanisms of oxidation have not yet been fully characterized, the reaction rates appear to be influenced by surface adsorption, in addition to bulk diffusion [1,2]. The task of constructing an optimal high-temperature processing schedule is, therefore, complicated by the fact that porosity and surface conditions strongly influence oxidation. An additional complication arises from the fact that, while the diffusion and adsorption rates increase with increasing temperature, the equilibrium oxygen concentration in the material decreases with increasing temperature, so that, after the final annealing, cooling must proceed slowly enough to allow adequate absorption to occur.