Role of calcium in the evolution of superconductivity in a (La2-xRx)Ba2(CayCu4+y)Oz (R = Y, Er, Gd) system

Abstract

It has been reported that, by adding equal amounts of CaO and CuO to non superconducting La3Ba3Cu6O z (La-336), a series of superconductors with nominal compositions La3Ca y Ba3Cu6+yO z were prepared with maximum Tonc ∼ 80K. Similar studies on addition of CaO and CuO in nonsuperconducting LaBaCu2O z (La-112) resulted into superconducting LaCaBaCu3O z (La-1113). To date no attempt has been made to synthesize La2CaBa2Cu5O z (La-2125) superconducting phase by addition of CaO and CuO to non superconducting La2Ba2Cu4O z (La-224) system. Also no reports are published to study the effect of replacing larger La3+-ions (1.01A) by smaller rare earth ions viz Y3+(0.89A), Er3+(0.91A), Gd3+(0.91A) on the structural and superconducting properties of (La2−xR x )Ba2(Ca y Cu4+y)O z (LRBCaC); 0.0 ≤ x ≤ 0.5; y=2x system. In this paper, we report the method of synthesis, structural and superconducting property characterization using X-ray diffraction, oxygen content measurements using iodometry, resistivity measurements using d.c. four probe technique and a.c. susceptibility measurements in the temperature range RT to 15K. Also a comparative study, on the evolution of superconducting phase with Ca-concentration for different rare earth substitutions for LRBCaC system in the context of hole doping mechanism, is carried out.