High-Pressure Structural Evolution of a Fluorocuprate Ruddlesden-Popper Phase

Ruddlesden-Popper (RP) based phases have piqued the interest of many scientists for decades since the discovery of superconductivity in the La2CuO4, hole-doped systems. Whilst there has been countless studies on the A2(Cu,Ni)O4+𝛅 systems, their fluoride counterparts (where A = K, Rb) have received far less attention, largely due to the stability of the I4/mmm structure with decreasing temperature, thereby not affording the phase transitions associated with the onset of superconductivity in the oxides. We have recently synthesised Na2CuF4 (monoclinic, P21/c) through HF-free synthesis routes, and expect to observe a phase transition to the RP phase under pressure. Our DFT calculations have shown that there is a lower energy ground state (P42/ncm) that is thermodynamically more stable than the monoclinic structure, which we expect to observe under high pressures. Here we propose a high pressure in-situ diffraction study on PEARL to investigate this phase transition, and its stability post-transition as the pressure is released.