ROLE OF OXYGEN IN LN(2-X)CE(X)CUO4 SUPERCONDUCTORS

The presence of more basic La3+ in the electron-doped LaNd1-xCexCuO4 Superconductors enhances the dissolution of the samples during iodometric analysis, which allows a precise determination to be made of the oxygen contents and their correlation to observed properties. The as-prepared LaNd1-xCexCuO4+delta samples all have 0 < delta less-than-or-equal-to 0.02 excess oxygen in the octahedral interstitial sites, which needs to be removed to achieve superconductivity. It becomes increasingly difficult to create oxygen vacancies as the Ce content in LaNd1-xCexCuO4 increases due to a decreasing internal stress resulting from an improved bond-length matching. An equilibrium in the oxygen occupancy between the octahedral interstitial and the tetrahedral sites necessitates the creation of 0 < delta < 0.03 oxygen vacancies in the tetrahedral sites of LaNd1-xCexCuO4-delta before all the interstitial oxygen atoms could be removed. This results in the absence of superconductivity at or above the nominal oxygen content 4.00.