SYNTHESIS, CHARACTERIZATION, AND SUPERCONDUCTING AND MAGNETIC-PROPERTIES OF ELECTROCHEMICALLY OXIDIZED LA2CUO4+DELTA AND LA2-XSRXCUO4+DELTA(0.01-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.33,0.01-LESS-THAN-OR-EQUAL-TO-DELTA-LESS-THAN-OR-EQUAL-TO-0.36)

La2CuO4 can be electrochemically oxidized in aqueous base at 295 K to form a superconductor with T(c) almost-equal-to 44 K [Wattiaux et al., C.R. Acad. Sci. (Paris) 310 (1990) 1047]. We have confirmed and extended this study. We conclude that the electrochemical reaction forms La2CuO4+delta. Two distinct bulk superconducting phases are found at delta almost-equal-to 0.03 (T(c) almost-equal-to 32 K) and delta greater-than-or-similar-to 0.08 (T(c) almost-equal-to 45 K). Bulk superconductivity is found in similarly prepared La2-xSrxCuO4+delta with T(c) almost-equal-to 40 K for 0.01 less-than-or-equal-to x less-than-or-equal-to 0.15. Normal state magnetic susceptibility data for La2CuO4.11 and La1.92Sr0.08CuO4.07 are nearly identical with those of conventionally prepared La1.85Sr0.15CuO4, indicating that the hole doping level (p) in the CuO2 planes of the three compounds is nearly the same. Iodometric titration experiments confirmed that the maximum doped-hole concentration from combined Sr-doping and electrochemical oxygen doping for 0 less-than-or-equal-to x less-than-or-equal-to 0.15 is p almost-equal-to 0.16 holes/formula unit. The electrochemical oxidation of the starting materials does not appear to be reversible.