PHASE-SEPARATION IN LA2CUO4+DELTA AS PROBED BY IMPEDANCE SPECTROSCOPY

The dc-conductivity and the high-frequency capacity of a La2CuO4+delta single crystal are determined by impedance spectroscopy in the freque ncy range 20Hz - 1MHz at liquid helium temperature. Using isochronal a nnealing, the effect of the phase separation on these quantities is st udied for E parallel and perpendicular to the CuO2-planes as well as f or different oxygen doping levels, delta, of the sample. The results a re consistent with the model of a diffusion controlled formation of a metallic - and below T-c superconducting percolation network in an ins ulating background.