  Pd site doping effect on superconductivity was investigated in
quasi-one-dimensional superconductor Nb2(Pd1-xRx)0.76S5 (R=Ir, Ag) by measuring
resistivity, magnetic susceptibility and Hall effect. It was found that
superconducting transition temperature (Tc) is firstly slightly enhanced by
partial substitution of Pd with Ir and then it is suppressed gradually as Ir
content increases further. Meanwhile Ag substitution quickly suppresses the
system to a nonsuperconducting ground state. Hall effect measurements indicate
the variations of charge carrier density caused by Ir or Ag doping. The
established phase diagram implies that the charge carrier density (or the band
filling) could be one of the crucial controlling factors to determine Tc in
this system.
