Chemical Interaction between High-Tc Superconducting Oxides and Alkaline Earth Fluorides

Abstract
Reactions of high-T c superconductors and MF2 (M: Ca, Sr, Ba) were investigated by means of ac susceptibility, X-ray diffraction, and TG-DTA measurements. The superconducting transition temperature (T c onset) of Ba2YCu3O7-δ powder mixed with MF2 powder decreased as a result of heat treatment at 600°C in air, whereas it did not decrease by the heat treatment under carefully dried conditions. In contrast, neither of the heat-treatment conditions decreased the T c onset of Bi2Sr2CaCu2O x mixed with MF2 powder. Heating with MF2 at temperatures higher than 700°C reduced volume fractions of these superconductors even in dry atmosphere and the reactivity increased in the order of BaF222 for Ba2YCu3O7-δ, and SrF2\lesssimCaF22 for Bi2Sr2CaCu2O x .