Highly regular dislocation networks in superconducting Bi2Sr2CaCu2Oy s
ingle crystals have been observed by means of transmission electron mi
croscopy. A model describing their geometrical configuration, Burgers
vectors, and formation mechanism is presented. The ratio of the stacki
ng fault energy to shear modulus has been estimated. Such networks are
suggested as possible planar pinning centers for flux in the supercon
ducting state.