The pristine sample was characterised with XRD and Mössbauer spectroscopy (MöS, detailed in S2) to obtain the structure and composition. The as synthesised sample had a high sodium content and few vacancies and was a two-phase mix between the rhombohedral (𝑹𝟑) and the cubic (𝑭𝒎𝟑𝒎) structure (30:70). Details about the obtained composition and structure can be found in S1 and S2.