Preparation of n-type YBa₂Cu₃O_y films by an electrochemical reaction method

We report on the continuous carrier control from holes to the electrons in YBa₂Cu₃O_y (YBCO) films by an electrochemical reaction method. In this method, the reduction in the hole concentration or the electron doping occurs at room temperature simply by applying a voltage of ∼1 V between the YBCO film and the Pt electrode in the electrolyte solution of AC1O₄ /polyethylene oxide, where A K or Cs. When the initial sample is slightly overdoped, a dome-like increase and decrease of T_c and an increase of resistance R and Hall coefficient R_H, which correspond to a reduction in the hole concentration to ∼10²¹ cm^-3, are observed with increasing voltage or application time. These results suggest that this electrochemical method is a straightforward and effective method for electron doping. Starting with a heavily underdoped sample, which is not superconductive, we succeeded in changing the sign of R _H from positive to negative and in rapidly reducing R.