Chemical Doping and Career Tuning in Ni-site Substituted Layered Nickelates Pr4Ni3-xMxO8 (M: 3d Transition Metals) Studied by X-ray Absorption Spectroscopy

Layered nickelate R4Ni3O8 (R = La, Pr, Nd, Sm) is a candidate for a high-temperature superconductor because its crystal structure and electronic state are very similar to high-temperature superconducting cuprates (HTSC). We have performed carrier tuning by chemical substitution to Ni sites to bring the electronic states of Ni closer to that of Cu in HTSC. In this study, we synthesized the Pr4Ni3O8 samples doped with Ti, Cr, and Cu for the Ni sites and investigated the valence states of these samples using X-ray absorption spectroscopy. Hole doping into Ni sites was suggested regardless of the dopant elements, according to the spectral change along the chemical substitutions, which may result from the involvement of dopants in electrical conduction and changes in the electronic state of Ni and O. Superconductivity is not observed down to 2 K, suggesting that the Ni 3d electron numbers do not fall within the appropriate range for emerging superconductivity.