We present an infrared transmission Pr 3ϩ crystal-field study of as-grown, reduced, and oxygenated Pr 2Ϫx Ce x CuO 4Ϯ␦ single crystals and thin films. Excitations from the ground-state multiplet 3 H 4 to the 3 H 5 , 3 H 6 , 3 F 2 , and 3 F 3 excited multiplets are observed in all samples. In addition to the Pr 3ϩ regular sites, which remain unperturbed following the cerium doping or the oxygen content modifications, Pr 3ϩ sites are detected. A precise set of crystal-field parameters, which reproduces the energy and the symmetry of the levels, is determined. The reduction process, which drives the electron-doped cuprates superconducting, is discussed in detail and scenarios for the reduction mechanism and induced vacancies are proposed. In contrast to the common belief, the apical oxygen, which is clearly detected in all samples, is not removed in Pr 1.85 Ce 0.15 CuO 4 following reduction. This observation questions the role attributed to the apical oxygen removal in triggering the superconductivity.

No abstract

No abstract

No abstract

We report a neutron and Raman scattering study of a single-crystal of La2CuO4.05 prepared by high temperature electrochemical oxidation. Elastic neutron scattering measurements show the presence of two phases, corresponding to the two edges of the first miscibility gap, all the way up to 300 K. An additional oxygen redistribution, driven by electronic energies, is identified at 250 K in Raman scattering (RS) experiments by the simultaneous onset of two-phonon and two-magnon scattering, which are fingerprints of the insulating phase. Elastic neutron scattering measurements show directly an antiferromagnetic ordering below a Néel temperature of TN = 210 K. The opening of the superconducting gap manifests itself as a redistribution of electronic Raman scattering below the superconducting transition temperature, Tc = 24 K. A pronounced temperature-dependent suppression of the intensity of the (100) magnetic Bragg peak has been detected below Tc. We ascribe this phenomenon to a change of relative volume fraction of superconducting and antiferromagnetic phases with decreasing temperature caused by a form of a superconducting proximity effect.