Superconductivity in Alkaline Earth-Substituted La 2 CuO 4-y

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Abstract
La 2 CuO 4- y ceramics containing a few percent of Ca 2+ , Sr 2+ , and Ba 2+ ions have been prepared. Resistivity and susceptibility measurements exhibit superconductive onsets (as in earlier Ba 2+ -containing samples). The onset temperature La 2 CuO 4- y with Sr 2+ is higher and its superconductivity-induced diamagnetism larger than that found with Ba 2+ and Ca 2+ . This is proof that the electronic change resulting from alkaline earthdoping, rather than the size effect, is responsible for superconductivity. The ionic radius of Sr 2+ is close to that of La 3+ for which it presumably substitutes.