Correlation of lattice parameter, oxygen content and charge carrier density in Nd 2−x−yLa yCe xCuO 4-δ superconductors

Abstract

The superconductivity of Nd 2−x−yLa yCe xCuO 4-δ (y=0∼1.2, x=0.15∼0.10) series is studied. The Tc decreases and lattice constant a increases with increasing La content and a fixed Ce content. However, the reduction of Tc induced by increasing lattice parameter a can be recovered by an appropriate decrease of Ce content in spite of the lattice parameter a up to 3.98Å. This indicates that the lattice parameters are not directly related to the superconductivity. Actually, both the change of Ce-doping and a parameter jointly induce a variation in oxygen vacancies and result in the change of charge carrier density. It implies that lattice parameters, doping effect, oxygen content and charge carrier density are interrelated and should be taken into unified account, in which the charge carrier density is a determining factor for superconductivity.