Synthesis of oxide superconductors by soft-chemical techniques

Our recent works on the synthesis of oxide superconductors using soft-chemical techniques are reviewed. First, Li-intercalation into layered perovskites has been carried out. We have found new Li-intercalated superconductors of the Ruddlesden-Popper phase of LixSr2CuO2X2 (X = Br, I) with Tc = 7–8 K and the Dion-Jacobson phase of LixASr2Nb3O10 (A = Rb, Cs) with Tc ∼6 K. However, no superconductivity has appeared in Aurivillius phases of LixBi4Ti3O10 and LixBi2MO6 (M = Mo, W). Next, we have succeeded in preparing insulating La2CuO4 with the Nd2CuO4-type (T′) structure and superconducting Ba0.6K0.4BiO3 by the direct precipitation from molten alkaline-metal hydroxides at a temperature as low as 260–350 °C.