LAYER BY LAYER PREPARATION OF (Y1-XPRX)BA2CU3O7 ALLOY THIN-FILMS

We report on a new way to prepare highly homogeneous high Tc alloy thin films. We use dc magnetron sputtering with two stoichiometric targets (YBa2Cu3O7 (YBCO) and PrBa2Cu3O7 (PrBCO)) to prepare (Y1 - xPrx)BCO alloys by sequentially depositing ultrathin layers (less than a unit cell) of both materials. With this technique we fill each rare earth (R) plane with the desired amount of Y and Pr. Using MgO substrates we get highly oriented alloys with the c-axis parameter perpendicular to the substrate. The superconducting transition can be adjusted between 90K and OK with transition widths as narrow as 2K. Resistively measured critical fields Hcr display a behavior rather similar to the one found in YBCO, but indicative of an activation energy for flux flow smaller than in YBCO. We find also in the alloy series that Hcr is proportional to ( 1-T Tc)α with an exponent different from the 3 2 observed in YBCO. © 1990.