An experimental study has been carried out on the relationship between Y2Ba1Cu1O5 particles in Y1Ba2Cu3Ox superconductors and electric furnace cooling rates. As the electric furnace cooling rates decrease, the Y2Ba1Cu1O5 particles become uniformly disperse in fluorine-doped Y1Ba2Cu3Ox superconductors. However, the Y2Ba1Cu1O5 particles do not appear in the undoped Y1Ba2Cu3Ox superconductors.