Study of pressure effect on Gd-doped La₃Ni₂O_7-δ

The discovery of superconductivity above 77 K in pressurized La₃Ni₂O₇ has reignited interest in nickelate analogs of cuprates, where the NiO₂ bilayers mirror the superconducting CuO₂ planes. While the La site is generally regarded as electronically inactive, its substitution by magnetic elements provides a route to probe lattice and magnetic effects on the emergent superconductivity. Here we synthesize and investigate La_3-xR_xNi₂O_7-δ (R = Gd, Sm) under high pressure. Low substitution levels stabilize the Amam phase with enhanced crystallinity, whereas higher substitution levels drive lattice distortions and symmetry transitions. High-pressure resistivity measurements reveal superconductivity with T_c up to 83 K near 37 GPa and pressure-induced anomalies around 14 GPa and 21 GPa, signaling structural transitions. Oxygen annealing improves metallicity and lowers the pressure for the onset of superconductivity. Despite the strong local moments of R, no long-range magnetic order appears, indicating that La is not essential for superconductivity in bilayer nickelates. These findings highlight the interplay among structure, magnetism, and pressure in stabilizing high-T_c phases beyond the parent La₃Ni₂O₇ system.