Influence of hole filling and pair breaking by Nd and hole doping by Ca onthe superconductivity of NdBa2Cu3Oz

The structural and superconducting properties of Nd- and Ca-substituted (Nd 1-xCax)(Ba2-yNdy)Cu3Oz samples prepared under identical conditions have bee n investigated by x-ray diffraction, resistivity, ac susceptibility and oxy gen content measurements. The effect of increasing Nd concentration in NdBa 2-yNdyCu3Oz lowers the carrier concentration and decreases T-c, which is at tributed to magnetic pair breaking by local moments and hole filling by Nd. This suppression in T-c has been compensated by appropriate hole doping wi th Ca in (Nd1-xCax) (Ba2-yNdy)Cu3Oz, which shows that for a fixed Nd conten t at the Ba site T-c increases dramatically as the Ca content increases. Fo r instance, in the oxide (Nd1-xCax)(Baz-yNdy)Cu3Oz, the T-c increases from 0.0 K (x = 0.0, non-superconductor) to 77.5 K (x = 0.4, compensated oxide) as the magnetic pair breaking and hole filling by Nd is nearly balanced by hole doping from Ca.