The modulation principle of vacuum on the superconductivity of YBCO

By neutron diffractions, and other experiments we have found that oxygen ions in YBCO can diffuse out of the sample in vacuo at room and low temperature, while the T c decreases greatly. We have also found that if the vacuum-deoxidation process lasts for several days there will be a damping oscillation of T c with time ( t), and higher vacuum corresponds to a greater amplitude and a shorter period. We tentatively think that T c should satisfy the following function: T c0∞ T ce −βtcos (ω t+ϕ); it may be due to the diffusion of oxygen and the saturation of the valence state.