Structural, transport, and magnetic properties of Pr 1.85Ce 0.15CuO 4− y prepared through different precursors

Abstract

Polycrystalline samples of the electron-doped high- T c superconductor Pr 1.85Ce 0.15CuO 4− y were prepared with different starting materials: (1) mixture of simple oxides Pr 6O 11, CeO 2, and CuO; (2) mixture of simple oxides Pr 6O 11 and CuO, and an intermediate compound PrCeO 2; and (3) from a sol–gel precursor. All the samples were sintered in air at temperatures below 1030°C and reduced under Ar atmosphere at 950°C. Observations of X-ray diffraction, electrical resistivity, ρ( T), and magnetization, M( T), indicate the important effects that Ce diffusion and homogeneity have upon the macroscopic properties of this compound. The kinetics of the phase formation was accompanied by measurements of X-ray powder diffraction. These measurements, along with the determination of the lattice parameters a and c of the tetragonal T′-structure of these compounds, revealed that a complete diffusion of Ce into Pr 2CuO 4− y is only observed in samples prepared through a sol–gel precursor. Electrical resistivity measurements are consistent with the X-ray data and show both higher and sharper superconducting transition temperatures T c i in sol–gel samples. Measurements of magnetization performed on either pellets and powders confirm the latter results and indicate that samples prepared through sol–gel route have larger diamagnetic susceptibility at low temperatures. In addition, qualitative arguments suggesting the importance of Ce stoichiometry in both the normal-state electrical resistance and the superconducting properties of these polycrystalline samples are discussed.