Structure and superconductivity of La₂PrNi₂O₇ under pressure

Nickel-based superconductors have attracted great attention due to the finding of the Ruddlesden–Popper (R–P) bilayer nickelate La₃Ni₂O₇ with superconducting critical temperature (T_c) of 80 K at pressure above 14 GPa. Recent efforts have been devoted to the study of La₂PrNi₂O₇, while the detailed structure remains unclear. In this work, we explore the stability and physical properties of such an interesting system by using density functional theory and the U parameter simulation method implemented in VASP. The results show that the enthalpy of La₂PrNi₂O₇ is slightly larger than its parent material bilayer R–P nickelate La₃Ni₂O₇. The electronic structure analysis indicates that near the Fermi level, the e_g orbit of Ni dominates and strongly hybridizes with the 2p orbit of O, thereby forming a significant van Hove singularity that is conducive to superconductivity. The Amam phase to the I4/mmm phase occurs, accompanied by an increase in the bandwidth of Ni 3d_z² and an enhancement of the bonding–antibonding splitting (from about 0.5 eV to 1.5 eV), which leads to an increase in the density of states at the Fermi level. Our findings provide insights into the preparation and superconductivity of R–P bilayer nickelate.