Correlation between synthesis, stoichiometry, structure and superconductivity of La2-xKxCuO4-δ

The low temperature synthesis of alkali substituted phases La2-xKxCuO4-delta with defined metal stoichiometry (0 less than or equal to x less than or equal to 0.25), copper oxidation state and superconducting properties from alkali hydroxide melts as well as thermal transformations with phase segregation are reported. Electron diffraction shows a deviation from the ideal K2NiF4 structure type. The occupation and distortions of the oxygen sublattice are discussed using neutron diffraction studies. In terms of superconducting properties a most unusual result is the observation that the nominal hole concentration for a given T-c value of the K doped phases is twice the concentration required in alkaline earth doped systems. (C) 1999 Published by Elsevier Science B.V. All rights reserved.