Traveling solvent floating-zone growth and reduction condition optimization of Nd 2− xCe xCuO 4 single crystals

Abstract

In order to find the optimal reduction conditions in Nd 1.85Ce 0.15CuO 4, we have grown high-quality Nd 1.85Ce 0.15CuO 4 single crystals by the traveling solvent floating-zone method and reduced them systematically by varying both the reduction temperature ( T reduction) and the reduction time ( τ reduction) while keeping the reduction atmosphere constant. The crystals reduced in a flowing Ar+O 2 gas mixture with an oxygen partial pressure of 9.6×10 −6 atm at T reduction=980°C for τ reduction=three days exhibited the optimum superconducting properties: T c =25.5 K and a superconducting volume fraction F SC=100%. It is suggested that the optimum reduction condition is located outside the field of stability in the phase stability diagram of Nd 1.85Ce 0.15CuO 4 but located near the boundary of the field of stability.