CARRIER-CONTROLLED DOPING EFFICIENCY IN LA2CUO4+DELTA

We have studied the excess oxygen content and hole concentration in 11 0 degrees C annealed La2CuO4+delta prepared by electrochemical oxidati on for 0 < delta < 0.12. Two distinct sites were observed with doping efficiency of 2 or 1.3 holes per excess oxygen atom. The occupation of the two different sites is determined by a critical carrier concentra tion P-c approximate to 0.06. As a consequence, a sudden increase of c hemical potential of doped holes at P-c is suggested.