Influence of hole-filling by La and hole-doping by Ca on the superconductivity of NdBa2Cu3O7−δ

The structural and superconducting properties of La- and Ca-substituted (Nd1−xCax)(Ba2−yLay)Cu3Oz samples prepared under identical conditions have been investigated by X-ray diffraction (XRD), resistivity, ac susceptibility and oxygen content measurements. The effect of increasing La-concentration in Nd(Ba2−yLay)Cu3Oz is in lowering the carrier concentration and decreasing Tc, which is attributed to hole-filling by La. This suppression of Tc has been compensated by appropriate hole-doping with Ca in (Nd1−xCax)(Ba2−yLay)Cu3Oz, which shows that for a fixed La content at Ba-site, Tc increases dramatically as the Ca content increases. For instance, in the oxide (Nd1−xCax)(Ba1.6La0.4)Cu3Oz, the Tc increases from 0.0 K (x=0.0, non-superconductor) to 84.0 K (x=0.4, compensated oxide) as the hole-filling by La is completely balanced by hole-doping from Ca.