Electrical and structural properties of ex-situ annealed superconducting $Bi_2Sr_2CaCu_2O_8$ thin films obtained by coevaporation of components

Özet

$Bi_2Sr_2CaCu_2O_8$ system superconducting thin films were obtained by synchronized deposition of Bi, Cu, $CaF_2$ and $SrF_2$ components onto cleaved MgO (100) single crystal substrates after annealing in the temperature range 600-840 °C. The films were annealed in H2O and O2, then dry O2 atmosphere for the removal of fluorine from the structure and to attain superconducting properties. X-ray powder diffraction patterns were used to characterize the obtained film structure. The films were observed to grow along c-axis perpendicular to the substrate surface with the identified reflection on the $(00{l}= 6, 8, 10 ... )$ planes. The films having the critical temperature higher than liquid nitrogen were obtained when Bi and the other components were evaporated from separate sources. DC resistance in the films were measured in the temperature range 77-300 K. of those films having good superconducting properties, metallic behaviors were seen in the normal state and zero resistance at 79 K was obtained following a transition in the resistance.