HIGH OXYGEN-PRESSURE SYNTHESIS OF NEW COPPER-OXIDE SUPERCONDUCTORS

The unique coordination of the copper ions in +1, +2, and +3 oxidation states, which are stable in a range of oxygen partial pressure, 10(-6 ) < P(O2) < 10(3) atm, makes possible the formation of a wide variety of distinct structures. By controlling the oxygen pressure during the synthesis and annealing, the distribution of metal and oxygen ions can be modified on an atomic scale to optimize the structural and electro nic properties. We present several examples of compounds for which the critical structural elements for superconductivity, i.e., the perfect ly ordered CuO2 planes, have been obtained and doped with holes by mea ns of high oxygen pressure, P(O2) > 1 atm. These materials, La2CuO4+de lta, La2-xCaxCuO4, and YSr2-xLaxCu3O7+delta, offer a unique opportunit y to study the relationship between superconductivity and structural, magnetic, and chemical properties.