Superconductivity in alkaline earth-substituted La₂CuO _4-y

La2CuO4-y ceramics containing a few percent of Ca2+, Sr2+, and Ba2+ ions have been prepared. Resistivity and susceptibility measurements exhibit superconductive onsets (as in earlier Ba2+-containing samples). The onset temperature La 2CuO4-y with Sr2+ is higher and its superconductivity-induced diamagnetism larger than that found with Ba 2+ and Ca2+. This is proof that the electronic change resulting from alkaline earth-doping, rather than the size effect, is responsible for superconductivity. The ionic radius of Sr2+ is close to that of La3+ for which it presumably substitutes.