SYNTHESIS, SINGLE-CRYSTAL STRUCTURE, AND SUPERCONDUCTIVITY OF THE RUBIDIUM-SUBSTITUTED LA2CUO4

The new compound La2-xRbxCuO4 (x = 0.055(3)) has been synthesized thro ugh a low-temperature (<450-degrees-C) technique employing molten hydr oxide salts. For rubidium-doped La2CuO4, RbOH acts not only as a low-t emperature flux but also as a reactant that contributes the alkali met al to the final product. La1.945Rb0.055CuO4 crystallizes in the tetrag onal space group D4h17-I4/mmm with two formula units in a cell of dime nsions a = 3.7858(6) and c = 13.276(3) angstrom (T = 298 K). The struc ture has been determined by single-crystal X-ray diffraction methods. Superconductivity is observed for the first time in the La2-xRbxCuO4 s ystem with a T(c onset) almost-equal-to 22 K for x = 0.055. This molte n-salts method was also employed to synthesize single crystals of sodi um- and potassium-substituted La2CuO4. These compounds exhibit superco nductivity with a T(c onset) of approximately 28 and 20 K, respectivel y.