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Inelastic x-ray scattering (IXS) with very high (meV) energy resolution has become a valuable spectroscopic tool, complementing the well established coherent inelastic neutron scattering (INS) technique for phonon dispersion investigations. In the study of crystalline systems IXS is a viable alternative to INS, especially in cases where only small samples are available. Using IXS, we have measured the phonon dispersion of Nd[SUB1.86]Ce[SUB0.14]CuO[SUB4+δ] along the [&xgr;, 0, 0] and [&xgr;, &xgr;, 0] in-plane directions. Compared to the undoped parent compound, the two highest longitudinal optical (LO) phonon branches are shifted to lower energies because of Coulomb-screening effects brought about by the doped charge carriers. An additional anomalous softening of the highest branch is observed around q = (0.2, 0, 0). This anomalous softening, akin to what has been observed in other compounds, provides evidence for a strong electron-phonon coupling in the electron-doped high-temperature superconductors. [ABSTRACT FROM AUTHOR]

We present here a study on the effect of Al doping on the structure of SmBa[SUB2]Cu[SUB3-x]Al[SUBx]O[SUB6+δ] (Sm-123) superconductor. Electron MicroProbe Analysis (EMPA) and X-Ray Powder Diffraction (XRPD) have revealed that the limit of aluminium solubility x is between 0.5 and 0.6. For further doping BaAl[SUB2]O[SUB4] appears besides the superconducting phase. XRPD analysis on samples annealed in both oxidising and reducing conditions have revealed that the Al doping inhibits the tetragonal to orthorhombic phase transition. Nuclear Magnetic Resonance (NMR) analysis has shown that almost all the Al ions are coordinated tetrahedrally. The comparison between oxygen non-stoichiometry in pure and Al doped SmBa[SUB2]Cu[SUB3-x]Al[SUBx]O[SUB6+δ] suggests that the Al ions are ordered in clusters. A model is proposed for short-range order around Al doping ions which allows us to interpret the phase transition inhibition. [ABSTRACT FROM AUTHOR]

We present here non-stoichiometry and electrical conductivity measurements in the low-T and highT range for the Eu[sub 1+x]Ba[sub 2-x]Cu[sub 3]O[sub y] system with x = 0, 0.2 and 0.4. We found an anomalous trend of the T[sub c] with y for EuBa[sub 2]Cu[sub 3]O[sub y] (Eu-123) relative to other HTSC of REBa[sub 2]Cu[sub 3]O[sub y] family (RE = Y, Nd, Sm). On the contrary high-T data for the whole system show a behavior similar to that of others RE-123. [ABSTRACT FROM AUTHOR]

The charge carrier density plays a crucial role in the transition between normal and superconducting state in the copper-oxide superconductors. In Nd[sub 1.85]Ce[sub 0.15]CuO[sub 4+δ] sample, for charge carrier density n = nc ... 0.07 the superconductivity sets in. In order to investigate the magnetic properties around nc, a set of magnetic susceptibility measurements in the temperature range 3-260K for samples with different charge carriers concentrations were realized. Magnetic susceptibility curves of Nd[sub l.85]Ce[sub 0.15]CuO[sub 4+δ revealed novel behavior well above the critical temperature T[sub c]: at fixed T≥45K, the susceptibility λ, reported as a function of the charge carrier density n, shows a peak around n=0.06 and drops to significantly lower values for n greater than 0.07, the value at which the samples become superconducting. The effective magnetic moment µ[sub eff] shows the same behavior. The comparison of the present experimental results with recent transport ones gives evidence of a possible interaction between charge carriers above T[sub c]. The possibility that this effect could be due to a bipolarons-like mechanism of charge carriers interaction is discussed. [ABSTRACT FROM AUTHOR]