${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_y$ (2212) films, grown in situ by laser ablation, show the presence of the intergrowth phenomenon: the random stacking of 2201 $\left({\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Cu}}_1{\mathrm{O}}_x\right)$ and 2212 cells. The precise fraction of the 2201 phase intergrowth depends on the growth conditions. We have measured the influence of such structural defects on electrical transport and magnetic properties. The main consequences of the intergrowth are a broadening of the superconducting transition and a decrease of the critical temperature. The irreversibility line of the films has been deduced from ac susceptibility measurements in magnetic fields $H$ parallel to the $c$ axis of the films using a superconducting quantum interference device magnetometer. A strong shift of the irreversibility line to low fields and temperatures is reported with increasing the percentage of 2201 stacking faults.

• Received 14 October 1997

DOI:https://doi.org/10.1103/PhysRevB.57.13811