Hall effect-in electrochemically oxidized La2CuO4+δ and (La1-xSrx)2CuO4+δ

We have prepared the superconducting La2CuO4+delta electrochemically oxidized at 333 K. Each sample is a single-phase superconductor; the low-T-c phase (T-c = 32 or 36 K, oxidation time - 24 h, delta = 0.068) or the high-T-c phase (45 K, 72 h, 0.093). We have studied the relation between the hole concentration n(H), determined by the Hall effect measurement as n(H) drop 1/eR(H) and the valence of Cu 2 + p, determined by the iodometric titration in La2CuO4+delta. In highly oxidized La2CuO4+delta, the p/2-dependence of n(H) has been found to be different from that of the ordinary (La1-xSrx)(2)CuO4. Similar phenomena were observed in (La1-xSrx)(2)CuO4+delta (x = 0.050, 0.075, 0.100) electrochemically oxidized at 333 K. These results suggest that in La2CuO4+delta or (La1-xSrx)(2)CuO4+delta, the intercalated excess oxygen plays a different role in conduction from Sr in the ordinary (La1-xSrx)(2)CuO4. (C) 2000 Elsevier Science B.V. All rights reserved.