Fluctuation‐induced conductivity of (YCe)Ba₂Cu₃O_7–δ superconductor

Abstract

Phone: þ55 42 220 3044, Fax: þ55 42 220 3042Systematic measurements of the in-plane and out-of-plane in conductivity fluctuations have been used to investigate the role of the cerium ion on the splitting of the pairing transition. This splitting, associated with a phase separation, was firstly observed in single crystals and polycrystalline samples of Y 1-x Pr x Ba 2 Cu 3 O 7-d . Considering that Ce is the rare-earth element most easily ionized to the þ4 state and that in melttextured sample, it is possible to observe anisotropic effects, we examined the effect of this ion in the Y 1-x Ce x Ba 2 Cu 3 O 7-d compound. We prepared three different samples: polycrystalline, pure melt-textured and Ce-doped melt-textured. Melttextured samples were prepared using the top-seeding growth technique and the polycrystalline sample by the standard solid-state reaction technique. The samples were characterized by X-ray diffraction, scanning electron microscopy (SEM) and electrical resistivity. To identify power-law divergences in the conductivity, the results were analyzed in terms of the temperature derivative of the resistivity (dr=dT) and of the logarithmic temperature derivative of the conductivity (ÀdlnðDsÞ=dT). In the normal phase, Gaussian and critical regimes were clearly seen for melt-textured samples and no important differences between pure and Cedoped samples were observed. On the other hand, for the polycrystalline sample and from the critical exponent analysis, a splitting of the pairing transition was clearly observed. It is suggested that the occurrence of a phase separation and its association with Ce doping as already observed for Pr-doped samples. form an important family of superconducting materials with critical temperatures around 92 K. RE signifies the rare-earth elements except for Ce, Pr, and Tb. These elements have in common the possibility of existing in a tetravalent state [1,2], and Ce, Pr, and Tb, in that order, are the three rare-earth elements most easily ionized to the þ4 state. Several explanations have been proposed for the absence of superconductivity and the depression of critical temperature T C in (Pr-Ce)Ba 2 Cu 3 O 7-d . Some studies suggest that a tetravalent ionic state would lead to compensation or back filling of holes in the CuO 2 planes introduced by oxygenation [3]. The effect of Ce substitution in the RE-123 has been discussed in the framework of the existing models for the Pr system, and besides the hole-filling model [3], some other models such as hole localization [4], magnetic pair breaking [5], and percolation [6] have been proposed to explain the degradation of superconductivity.

Splitting of the pairing transition and coherence transition in R1−xCexBa2Cu3O7−δ(R = Y, Er, Ho and Gd)

“…The splitting of the pairing transition has been observed also in other doped samples prepared by different thermal treatments such as in single crystal and polycrystalline samples of Y 1−x Pr x Ba 2 Cu 3 O 7−δ [10,11]. However, it has not been observed in pure YBa 2 Cu 3 O 7−δ (single crystal and polycrystalline samples) [20,21], in polycrystalline Tm 1−x Pr x Ba 2 Cu 3 O 7−δ [24] and in melt-textured Y 0.95 Ce 0.05 Ba 2 Cu 3 O 7−δ [25]. Therefore, the results obtained up to now clearly show that the ionic size of the rare earth element, the presence or not of Ce/Pr and the thermal route employed in sample preparation affect drastically the splitting of the pairing transition.…”

Annealing effect on the excess conductivity of Cu0.5Tl0.25M0.25Ba2Ca2Cu3O10−δ (M = K, Na, Li, Tl) superconductors

“…[1][2][3][4][5][6][7] These superconductors have great effects on superconducting order parameter fluctuation (SCOPF). In yttrium-based high temperature superconducting systems, the SCOPF is 3D in the mean-field regime, whereas in Bismuth based system it is essentially 2D.…”

Structural properties of hypothetical CeBa2Cu3O7 compound from LSDA+DMFT calculations

“…It was demonstrated that the partial substitution of Pr or Ce has a detrimental influence on sample conductivity and superconductivity, whereas Tb was found to substitute for Y without significant effects on either the normal state conductivity or T C [14]. Recently, it has been reported that (Y 1 − x Pr x )123 and (Y 1 − x Ce x )123 polycrystalline bulk samples exhibit two close and sharp genuine superconducting transitions as a consequence of the phase separation [15,16]. Ce takes a special place among the other rare-earths substituting for Y in the R123 family of compounds for one more reason.…”