Feasibility study for the detection of lead substitution sites in the hydroxyapatite crystal structure using high-resolution electron microscopy (HREM) at optimum focus
- 1 June 1986
- journal article
- Published by International Union of Crystallography (IUCr) in Journal of Applied Crystallography
- Vol. 19 (3) , 168-173
- https://doi.org/10.1107/s0021889886089719
Abstract
The theoretical feasibility of differentiating high-resolution electron microscope images obtained at Sherzer focus for two crystals of the same chemical composition [Pb6Ca4(PO4)6(OH)2] has been investigated for two commercially available electron microscopes: the Jeol 4000 EX microscope (Cs = 0.48 mm, V = 400 kV) and the Jeol 200 CX microscope (Cs = 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 [Pb6(2)Ca4(1)(PO4)6(OH)2] or evenly in both Ca sites [Pb3.6(2)Ca2.4(2)Pb2.4(1)Ca1.6(1)(PO4)6(OH)2]. Crystals of various thicknesses oriented along the [2{\bar 1}{\bar 1}0] 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.Keywords
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