Electron Irradiation Induced Transformation of (Pb 5 Ca 5 )(VO 4 ) 6 F 2 Apatite to CaVO 3 Perovskite

Crystallochemical changes of (Pb 5 Ca 5 )(VO 4 ) 6 F 2 apatite under electron irradiation were examined by transmission electron microscopy. The apatite, a synthetic analog of vanadinite, was moderately stable towards a less intense 300‐keV LaB 6 source, while it changed rapidly in structure when exposed to the higher flux of a 200‐keV field emission gun. The electron beam induced transformation of vanadinite proceeds sequentially by (i) migration and loss of fluorine, (ii) lead volatilization and conversion to 2–5‐nm platelets of a glaserite‐type structure, and (iii) the reduction of V 5+ to V 4+ with the removal of lead and calcium oxide that leads to single‐crystal CaVO 3 perovskite as the ultimate product. The phase transformations are interpreted based on the crystallographic relations among the CaVO 3 perovskite, the (Pb 5 Ca 5 )(VO 4 ) 6 F 2 apatite and the glaserite‐type structures, and compositional changes under electron irradiation.