Effect of potassium addition on YBa2Cu3Ox superconductors

Long period post-annealing in the oxygen atmosphere is necessary for YBa2Cu3Ox (Y123) bulk superconductors to impart superconductivity. We have investigated whether Y123 shows good superconductivity without oxygen annealing by potassium addition. If K+ ion substitutes on Ba2+ site since the size of K+ ion is close to that of Ba2+ ion, we can expect hole doping effect without additional oxygen annealing. We confirmed that the sample without potassium addition exhibited no superconductivity, while the sample with potassium addition had the onset Tc of above 90 K. This implies that the potassium addition certainly promotes the superconductivity of Y123.