The discovery of high-temperature superconductivity in pressurised La3Ni2O7 has generated signicant interest in Ruddlesden-Popper nickelates. However, the precise structural and chemical prerequisites for achieving bulk superconductivity remain a subject of intense investigation. Increasing evidence points to a complex materials landscape characterised by layer intergrowth and oxygen non-stoichiometry. While the La-Ni framework is established during high-temperature synthesis, the final electronic state is acutely sensitive to the thermodynamic history of the oxygen sublattice.

In this talk, I will discuss a systematic investigation into the thermodynamic stability of La3Ni2O7. We employ thermogravimetric analysis to identify the thermodynamic boundaries of La3Ni2O7 as a bilayer phase and to obtain precise control of its oxygen stoichiometry as a function of temperature and partial oxygen pressure. By establishing this thermodynamic control, we produce samples whose macroscopic physical properties as well as local electronic environment can be reliably interpreted and reproduced. Our approach provides a rigorous pathway toward defining the chemical and structural origins of the unconventional superconductivity in Ruddlesden-Popper nickelates.