Crystal Structure of Calcium-Deficient Carbonated Hydroxyapatite. Thermal Decomposition

✍ Scribed by T.I. Ivanova; O.V. Frank-Kamenetskaya; A.B. Kol'tsov; V.L. Ugolkov

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 513 KB
• Volume: 160
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2000.9238

✦ Synopsis

Full Rietveld re5nement of the crystal structure of the synthetic calcium-de5cient carbonated apatite Ca1 3.40 [Ca2 5.90 (NH 4 ) 0.10 ][(PO 4 ) 4.95 (CO 3 ) 1.05 (H 2 O) 0.30 ][(OH) 1.65 (H 2 O) 0.45 ] (space group P6 3 /m; a ‫؍‬ 9.437( 1), c ‫؍‬ 6.888(1) A > ; Z ‫؍‬ 1; R wp ‫؍‬ 5.23%) was carried out using X-ray powder di4raction data. The use of the model with the split position of O3 atom made it possible to 5nd two orientations of CO 3 triangles sharing one of their edges. They occupy randomly the adjacent faces of a PO 4 tetrahedron that are parallel to the c axis. O3c atoms coordinating carbon atoms are shifted by 0.37 A > from O3p atoms belonging to PO 4 tetrahedra. The charge unbalance occurring when [CO 3 ] 2؊ ions replace [PO 4 ] 3؊ groups is primarily compensated by vacancies in Ca1 sites. The studies of the sample thermal decomposition performed by simultaneous thermal analysis and by X-ray di4raction helped to analyze the localization and the amount of lattice water that enhanced the reliability of the structural model.