Dopant incorporation and anisotropy in in-plane aligned a-axis oriented YBa2Cu2.78Co0.22O7-delta thin films

We studied the effects of Co doping on the intrinsic anisotropic properties of in-plane aligned a-axis YBa2Cu3-xCoxO7-delta (x = 0.22) films, pulsed laser deposited on (100) LaSrGaO4 substrates. We used X-ray-absorption fine structure analysis and resistivity data to determine the quality of Co incorporation. The introduction of Co-dopant is believed to cause O disorder which leads to CuO chain fragmentation. Higher deposition pressures provided films with better Co incorporation but smaller grain size. However, at lower pressures proper Co incorporation can still be achieved by slowing down the post-deposition cooling rate. For transport along the c-direction, Co dopant causes an increase in resistive anisotropy (rho(c)/rho(b)) with increasing level of O ordering. Co doping level of x = 0.22 effectively doubles the resistive anisotropy of YBa2Cu3O7-delta films (from similar to 18 to similar to 40 at 100 K). (C) 1997 Elsevier Science B.V.