Site Preference of Rare Earth Elements in Hydroxyapatite [Ca10(PO4)6(OH)2]

✍ Scribed by Michael E. Fleet; Xiaoyang Liu; Yuanming Pan

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 211 KB
• Volume: 149
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8563

✦ Synopsis

Crystals of rare earth element-(REE)-bearing hydroxyapatites [La+OHAp, Nd+OHAp, Sm+OHAp, Dy+OHAp; Ca 10؊6x؊2y Na y REE 6x؉y (P 1؊x Si x O 4 ) 6 (OH) 2 , with x ‫؍‬ 0.036, y ‫؍‬ 0.045; space group P2 1 /b] have been grown from H 2 O-and Na-rich phosphate melts and their structures re5ned in space group P6 3 /m at room temperature with single crystal X-ray intensities to R ‫؍‬ 0.019+0.025. Hydrogen bond valences are in good agreement with a hydrogen-bonded model for the c-axis columns of OH ؊ ions. The crystal/melt partition coe7cients for REEs are 3.1, 3.3, 3.0, and 2.4 and REE site occupancy ratios (REE+Ca2/REE+Ca1) are 11, 2.0, 1.6, and 3.3, respectively. The uptake of REEs peaks at Nd, as in REE-substituted 6uorapatite (FAp). The REE site occupancy ratio in REE+OHAp and REE+FAp is proportional to the change in unit-cell volume, pointing to some control by spatial accommodation of substituents in the apatite structure. Both the site occupancy ratio and uptake are in6uenced also by the substitution mechanism, which varies with the volatile anion component.