Detailed structural analysis and the role of oxygen deficiency in the Nickelate superconductor, La3Ni2O7-δ

The recent discovery of superconductivity in Ruddlesden Popper (R-P) structured lanthanum nickelates has revitalised research into high-temperature superconductivity. In particular, La3Ni2O7 exhibits superconductivity near 80 K under uniaxial pressures of 15 to 40 GPa. Concurrent studies have revealed evidence of a charge density wave (CDW) a possible precursor to superconductivity under both ambient and pressurised conditions. However, the crystallographic and magnetic structures of La3Ni2O7 remain debated, with reports of bilayer (Cmcm) and monolayer trilayer (Fmmm) stacking polymorphs. Using high-resolution TEM, we have confirmed that our high-quality single crystals, grown by the floating zone method, adopt the monolayer trilayer structure. Preliminary neutron diffraction measurements (WISH, RB2500049) were inconclusive regarding CDW formation. We therefore propose a detailed structural investigation of the monolayer trilayer La3Ni2O7 polymorph using the SXD instrument to elucidate the role of nickel oxygen layering and oxygen defects in stabilising the CDW. Measurements will be performed across the CDW temperature range to identify possible structural anomalies. This study will provide essential insights into the structural origins of superconductivity in nickelates, utilising rare, high-quality single crystals and the advanced capabilities of SXD for precise structural determination.