Motivated by the recent observation of superconductivity with T_c ~ 80 K in pressurized La₃Ni₂O₇, the structural and electronic properties of A₃Ni₂O₇ bilayer nickelates (A = La-Lu, Y, Sc) were explored as a function of pressure (0–150 GPa) from first principles. A structural phase diagram was compiled that established chemical and external pressure as distinct and counteracting control parameters. Unexpected correlations were found between T_c and the in-plane Ni-O-Ni bond angles for La₃Ni₂O₇.

By disentangling the involvement of basal versus apical oxygen states at the Fermi surface, Tb₃Ni₂O₇ was identified as an interesting candidate for superconductivity at ambient pressure. These results suggest a profound tunability of the structural and electronic phases in this novel materials class and are key for a fundamental understanding of the superconductivity mechanism. The richness of the structural phase diagram and the unexpected transitions identified specifically for the later rare-earth nickelates provide additional opportunities for the discovery of superconducting phases.