Electron Irradiation Induced Transformation of (Pb5Ca5)(VO4)6F2 Apatite to CaVO3 Perovskite
نویسندگان
چکیده
Crystallochemical changes of (Pb5Ca5)(VO4)6F2 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 LaB6 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 to V with the removal of lead and calcium oxide that leads to single-crystal CaVO3 perovskite as the ultimate product. The phase transformations are interpreted based on the crystallographic relations among the CaVO3 perovskite, the (Pb5Ca5)(VO4)6F2 apatite and the glaseritetype structures, and compositional changes under electron irradiation.
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