OUT-OF-PLANE RESISTIVITY OF BI2SR2CACU2O8+X HIGH-TEMPERATURE SUPERCONDUCTOR

We have investigated the out-of-plane (c-axis) resistivity (rho(c)) of the Bi2Sr2CaCu2O8+x high temperature superconductor from the underdoped (x < 0) to the overdoped (x > 0) range. For the optimum doping (T(c) = 90 K) and for very thin samples (sample thickness d < 0.4 mum), usually we have found a metallic-like temperature dependence of the resistivity (drho(c)/dT > 0), while for bulk samples (d > 1 mum) and for underdoped samples rho(c) was semiconducting-like (drho(c)/d T < 0). A bulk sample, initially having drho(c)/dT < 0, on oxygen overdoping becomes metallic-like.