Reduction step and quenching of superconductivity in Nd1.85Ce0.15Cu1.01Oy:A Raman scattering study - art. no. 184503

The superconducting properties of the electron doped materials L2 - x(Ce,Th )(x)CuOy (L = Nd, Sm, Pr, and Eu) are extremely sensitive to small variatio ns of the oxygen content. Superconductivity only appears in samples that ar e quenched under slightly reduced atmospheres. at oxygen partial pressures below a critical value corresponding to the CuO-Cu2O equilibrium. We presen t a detailed Raman scattering investigation of Nd1.85Ce0.15Cu1 + dOy cerami c and single crystalline samples prepared under controlled oxygen content a bove and below this critical oxygen partial pressure. The Raman scattering spectra show that CuO traces are present in all the samples prepared above the critical partial pressure and discontinuously disappear for the superco nducting compounds. These results suggest that CuO might intergrow with the CuO2 planes in these compounds leading to a subtle internal strain that qu enches the superconducting state.