Effect of vanadium doping on the electrical and structural properties of GdBa₂Cu_3–xV_x O_7–δ

Abstract

The compounds with composition GdBa2Cu3–x Vx O7–δ and x = 0.0, 0.05, 0.1, 0.15, 0.2 and 0.3 have been prepared by the solid‐state reaction method. The XRD spectra indicate single‐phase formation of the compounds. The transition temperature decreases considerably with vanadium concentration to Tc = 26.4K for x = 0.3. The host sample is in the orthorhombic phase, but by increasing the V content the structure approaches the tetragonal phase, and for x = 0.3 the structure is nearly tetragonal. The normal state resistivity has been compared with 2D‐VRH, 3D‐VRH, and CG regimes, which shows that the 2D‐VRH and CG are in better agreement for our samples. The localization length is calculated for the 2D‐VRH, which shows a decrease with doping, and for x = 0.15 this drop is significant. Based on our preparation conditions, V is likely to remain as V4+ in the compound, and because of the high tendency of V4+ for achieving the octahedral structure, it appears that vanadium enters the chains, and accounts for the observed changes in the crystal structure and the superconducting properties. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Possible propagation of the Zhang–Rice singlet as a probable Cooper channel in the CuO2 planes

“…However, the inclusion of the strong correlations effect by appropriate doping can be used to correct this defect as W ≈ 1 eV for x = 0.4 for the common values (J dp /t pd = 0.3) and W ≈ 1 eV for x = 0.3 for J dp /t pd = 0.2 . This is quite encouraging as it has been earlier demostrated that the Gutzwiller projected d-wave pairing state is most stable for x ≤ 0.4 [21] which is a fair generalization since that of the cuprates is only stable up to x = 0.3 generically [23,24]. The only exception is the Y-Ba-Cu-O samples which has an additional 1D Cu-O chains that plays a role but is not taken into account in most calculations in 2D model.…”