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Feasibility study for the detection of lead substitution sites in the hydroxyapatite crystal structure using high‐resolution electron microscopy (HREM) at optimum focus
Author(s) -
Brès E. F.,
Voegel J. C.,
Barry J. C.,
Waddington W. G.,
Frank R. M.
Publication year - 1986
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889886089719
Subject(s) - electron microscope , resolution (logic) , crystallography , microscope , bar (unit) , scanning electron microscope , chemistry , crystal structure , analytical chemistry (journal) , materials science , high resolution , crystal (programming language) , optics , geology , physics , oceanography , remote sensing , chromatography , artificial intelligence , computer science , composite material , programming language
The theoretical feasibility of differentiating high‐resolution electron microscope images obtained at Sherzer focus for two crystals of the same chemical composition [Pb 6 Ca 4 (PO 4 ) 6 (OH) 2 ] has been investigated for two commercially available electron microscopes: the Jeol 4000 EX microscope ( C s = 0.48 mm, V = 400 kV) and the Jeol 200 CX microscope ( C s = 1.2 mm, V = 200 kV) and at the following resolutions: 1.4, 2.0 and 2.5 Å. In these crystals the lead atoms are distributed either preferentially in the Ca(2) sites [Pb 6 (2)Ca 4 (1)(PO 4 ) 6 (OH) 2 ] or evenly in both Ca sites [Pb 3.6 (2)Ca 2.4 (2)Pb 2.4 (1)Ca 1.6 (1)(PO 4 ) 6 (OH) 2 ]. Crystals of various thicknesses oriented along the [20] crystallographic direction have been investigated. The results show differences between images of the two structures, which are more marked when the crystal thickness is increased. A compromise between medium and ultra‐high resolution had to be reached for interpretation of the images.