Topotactic Hydrogen in Nickelate Superconductors and Akin Infinite-Layer Oxides ABO2

Superconducting nickelates appear to be difficult to synthesize. Since the chemical reduction of ABO(3) [rare earth (A), transition metal (B)] with CaH2 may result in both ABO(2) and ABO(2)H, we calculate the topotactic H binding energy by density functional theory (DFT). We find intercalating H to be energetically favorable for LaNiO2 but not for Sr-doped NdNiO2. This has dramatic consequences for the electronic structure as determined by DFT + dynamical mean field theory: that of 3d(9) LaNiO2 is similar to (doped) cuprates, 3d(8) LaNiO2 H is a two-orbital Mott insulator. Topotactic H might hence explain why some nickelates are superconducting and others are not.