Effect of light rare earth doping in 123 high temperature supercoductors

We have studied the structural and electrical properties of Gd(Ba2-xLax)Cu3O7+δ [Gd(BaLa)123], Gd(Ba2-xNdx)Cu3O7+δ [Gd(BaNd)123], and Nd(Ba2-xPrx)Cu3O7+δ [Nd(BaPr)123] compounds with 0.0≤x≤0.8 prepared by the standard solid-state reaction. The XRD patterns show that all of the samples with x≤0.5 are isosructure 123 phase, but in Gd(BaNd)123 and Nd(BaPr)123 there are several impurity peaks in the XRD patterns for x≥0.6. We estimated the xcsolubility=1.1, 0.6 and 0.55 in Gd(BaLa)123, Nd(BaPr)123, and Gd(BaNd)123, respectively. The resistivity increases with the increase of doping. The decrease of Tc with the increase of Pr doping is faster than Nd and La doping. The normal-state resistivity is fitted for two and three dimensional variable range hopping (2D&3D-VRH) and Coulomb gap (CG) regimes, separately. Our results indicate that the dominant mechanism for x≥xcSIT is 3D-VRH. The broadening of magnetoresistance have been investigated by TAFC and AH models. The pinning energy and Josephson coupling energy, decrease with the increase of applied magnetic field as U~H-β, these values also decrease with doping concentration Pr is more effective than Nd and La.