R 4 Ni 3 O 8 (R: rare-earth) is a candidate for high-T c superconductor because its crystal structure and electronic state are very similar to high-T c cuprates. Our recent works have pointed out that, by intercalation-deintercalation treatment with sulfur, the additional oxygen which impedes the metallic conduction is removed and the metallic behavior shows up in Nd 3.5 Sm 0.5 Ni 3 O 8. However, the semiconducting tendency remains below about 20-40 K, suggesting that the removal of additional oxygen is not complete. In this study, Pr-doping to Nd site in Nd 4 Ni 3 O 8 was performed in order to completely remove additional oxygen. By Pr-substitution, the electrical resistivity decreases and maintains metallic behavior down to low temperature (2 K). Next, we performed carrier tuning by chemical substitution to Ni sites in order to bring the electronic states of Ni closer to that of Cu in high-T c cuprates. Although the resistivity increases by doping, metallic behavior is maintained, suggesting that the dopants might occupy the specific Ni sites. However, superconductivity is not observed down to 2 K.

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