No abstract

In order to study the structure and dynamics of calcium–lead hydroxyapatites, Ca10−xPbx(PO4)6(OH)2, the Raman spectra of Pb10(PO4)6(OH)2 and Ca4Pb6(PO4)6(OH)2 are presented between 300 and 650 K in the 4000–10 cm−1 wavenumber range. For the two compounds, structural phase transitions are evidenced. The reversible structural transformation from monoclinic to hexagonal observed for Pb10(PO4)6(OH)2 occurs in two steps at 420 and 510 K. The hexagonal structure was not evidenced in the lead–calcium compound and only the first transition was observed near 420 K. At room temperature, OH− ions in pure lead hydroxyapatite (monoclinic form) are fully ordered within c‐axis columns. An increase in temperature leads to a progressive disordering of these anions, resulting in the stabilisation of the hexagonal phase. Ca4Pb6(PO4)6(OH)2 has a disordered structure at room temperature compared with pure lead hydroxyapatite. The two broad ν OH− bands observed at 3567 and 3582 cm−1 confirm this interpretation. The existence of hydrogen bonds between the OH− and the nearest PO43− is also confirmed with Raman spectroscopy. Copyright © 2001 John Wiley & Sons, Ltd.

No abstract

No abstract