Neutron Diffraction Study of Layered Nickelates Pr4Ni3−xCoxO8 for High-Temperature Superconductor Candidate

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. We have performed carrier tuning by chemical substitution to Ni sites to bring the electronic states of Ni closer to that of Cu in superconducting cuprates. We aim to substitute the specific Ni sites for carrier tuning without disturbing the NiO2 planes. In this study, we perform neutron powder diffraction experiments for the Pr4Ni3−xCoxO8 samples with doping Co for Ni sites to investigate the dopant distribution among the Ni sites. Rietveld analysis showed a tendency to preferentially occupy specific Ni sites when the doping level was low, but this is not the case for higher doping levels. We also analyzed the oxygen deficiency and found no oxygen deficiency in the NiO2 planes with lower chemical substitutions, indicating that the relatively undisturbed conduction planes were maintained. Finally, we discuss the effects of Co doping into NiO2 planes for the physical properties of R4Ni3O8.