Preparation ofn-type YBa₂Cu₃O_yfilms by an electrochemical reaction method

We report on the continuous carrier control from holes to the electrons in YBa(2)Cu(3)O(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 similar to 1 V between the YBCO film and the Pt electrode in the electrolyte solution of AClO(4)/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 similar to 10(21) 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.