Effect of Hole Density on Superconductivity in the Nd-Ce-Sr-Cu-O System

Abstract
Superconductivity of a solid solution with the composition of (Nd0.8-x Ce x Sr0.2)2CuO y was investigated. This phase is a prototype superconductor which has single-layered CuO square-pyramidal unit. A single-phased sample was obtained in a narrow range of Ce content, 0.0875≤x≤0.1500. Oxygen content and Ce valence were determined by two kinds of coulometric titration techniques. The results show that all samples have oxygen vacancies and that Ce is tetravalent. The critical temperature rises with an increase in hole density, which is determined by titration.