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

The structural and superconducting properties of La- and Ca-substituted (Nd 1-xCax)(Ba2-yLay)Cu3Oz samples prepared under identical conditions have bee n investigated by X-ray diffraction (XRD), resistivity, ac susceptibility a nd oxygen content measurements. The effect of increasing La-concentration i n Nd(Ba2-yLay)Cu3Oz is in lowering the carrier concentration and decreasing T-c, which is attributed to hole-filling by La. This suppression of T-c ha s been compensated by appropriate hole-doping with Ca in (Nd1-xCax)(Ba2-yLa y)Cu3Oz, which shows that for a fixed La content at Ba-site, T-c increases dramatically as the Ca content increases. For instance, in the oxide (Nd1-x Cax)(Ba1.6La0.4)Cu3Oz, the T-c increases from 0.0 K (x = 0.0, non-supercond uctor) to 84.0 K (x = 0.4, compensated oxide) as the hole-filling by La is completely balanced by hole-doping from Ca. (C) 1999 Elsevier Science B.V. All rights reserved.