Since the Bi-containing phases carry different volumes per Bi (Table in this work) and room temperature used for ex-situ characterizations. For example, orthorhombic BiF3, the thermodynamically most stable phase at room temperature and ambient pressure, can transform into trigonal BiF3 (space group P-3c1) under high pressure or after high energy (1100 rpm) ball milling; milder ball milling (600 rpm), as well as soft (350 °C) heat treatment, can recover the orthorhombic phase from the trigonal one . Cubic BiF3 which has the highest crystal density can be synthesized by precipitating dissolved bismuth nitrate from glycerin by adding a sodium fluoride solution . And it is also observed when gently (~120 °C) heating the orthorhombic form under vacuum . Given these structural variations, one should consider that the requirement of cooling the cell and thus the sample Though most of the reflections can be assigned to the phases observed in the ex-situ study discussed in section 3.2, two remarkable observations are made exclusively in the operando analysis and will be described in the following.