SUPERCONDUCTIVITY AND ANTIFERROMAGNETISM IN LA2-XCA1+XCU2O6+/-DELTA AND LA2-XSRXCACU2O6+/-DELTA

La2CaCu2O6 can be made superconducting by doping Ca or Sr in the form of La2-x(Sr,Ca)xCaCu2O6+delta and by synthesis under high O2 pressures of more than 4 atm. Superconducting properties of La2-xCa1+xCu2O6+/-delta (0.08 less-than-or-equal-to x less-than-or-equal-to 0.25) and La2-xSrxCaCu2O6+/-delta (0.07 less-than-or-equal-to x less-than-or-equal-to 0.23) as functions of composition (x) and oxygen partial pressure during synthesis (P(O2) up to 400 atm) were investigated by measuring their electrical resistivity and magnetic susceptibility. In both compounds, the superconducting transition temperature (T(c)) increased with increasing x and P(O2), and showed almost the same maximum T(c) (zero) of about 51 K at the solubility limit of Ca or Sr in La (x almost-equal-to 0. 25) with P(O2) at 400 atm, although at a lower P(O2), T(c) (zero) was higher in a Sr-doped compound than that of a Ca-doped compound. Nonsuperconducting or weakly superconducting La2-xCa1+xCu2O6+/-delta and La2-xSrxCaCu2O6+/-delta synthesized under oxygen partial pressures between 0.2 and 10 atm showed cusps in their magnetic susceptibility at around 25 K, which may result from three-dimensional (3D) antiferromagnetic ordering. The superconductivity of these compounds may appear as a result of the frustration of such 3D antiferromagnetic correlation as with other copper oxide superconductors.