Electron irradiation induced transformation of (Pb5Ca5)(VO4)6F2 apatite to CaVO3 perovskite

• Main Authors: Sun, K., Wang, L. M., Ewing, Rodney C., Dong, Zhili, White, Timothy John
• Other Authors: School of Materials Science & Engineering
• Format: Article
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Materials
• Online Access: https://hdl.handle.net/10356/95673; http://hdl.handle.net/10220/9478
• Institution: Nanyang Technological University

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 V5+ to V4+ 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 glaserite-type structures, and compositional changes under electron irradiation.