Nanocrystalline CaF2 powder specimens were produced both by co-precipitation of CaCl2 and NH4F and by ball milling of a coarse powder. The specimen homogeneity and a detailed picture of the lattice defects can be assessed by the simultaneous analysis of the powder diffraction pattern and of the solid-state 19F magic angle spinning NMR T1 relaxometry data. While diffraction line profiles provide information on domain size distribution and the content of dislocations, T1 relaxometry is more sensitive to inhomogeneity of the powder (large defect-free grains versus defective small ones). After extensive milling it is possible to obtain fluorite domains of comparable size to the chemically synthesized CaF2 (circa 10-12 nm), but with a marked difference in the lattice defect types and content. It is then proved that surface defects (related to domain size), line defects (dislocations) and point (Frenkel) defects have a quite different effect on the powder pattern as well as on the T1 spin-lattice relaxation time.

Combined X-ray diffraction and solid-state19F magic angle spinning NMR analysis of lattice defects in nanocrystalline CaF2

Ahmed Mahmoud Abdellatief, Mahmoud;Abele, Matthias;Leoni, Matteo;Scardi, Paolo
2013

Abstract

Nanocrystalline CaF2 powder specimens were produced both by co-precipitation of CaCl2 and NH4F and by ball milling of a coarse powder. The specimen homogeneity and a detailed picture of the lattice defects can be assessed by the simultaneous analysis of the powder diffraction pattern and of the solid-state 19F magic angle spinning NMR T1 relaxometry data. While diffraction line profiles provide information on domain size distribution and the content of dislocations, T1 relaxometry is more sensitive to inhomogeneity of the powder (large defect-free grains versus defective small ones). After extensive milling it is possible to obtain fluorite domains of comparable size to the chemically synthesized CaF2 (circa 10-12 nm), but with a marked difference in the lattice defect types and content. It is then proved that surface defects (related to domain size), line defects (dislocations) and point (Frenkel) defects have a quite different effect on the powder pattern as well as on the T1 spin-lattice relaxation time.
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Ahmed Mahmoud Abdellatief, Mahmoud; Abele, Matthias; Leoni, Matteo; Scardi, Paolo
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11572/33144
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