The method of point laser heating of a sample is used to perform experiment
al investigations of the electrical conductivity of YBa2Cu3O7 - x ceramic i
n the vicinity of its critical state. It is found that, in the vicinity of
transition to the superconducting state, the electrical conductivity of the
ceramic exhibits a clusterlike behavior substantially nonuniform over the
sample cross section. The topology of a superconducting cluster is investig
ated, as well as its spatial localization in the sample. A model of the for
mation of a superconducting cluster in a ceramic superconductor is suggeste
d. (C) 2000 MAIK "Nauka/Interperiodica".