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Monoclinic to hexagonal phase transition and hydroxyl motion in calcium–lead hydroxyapatites studied by Raman spectroscopy
Author(s) -
Hadrich A.,
Lautié A.,
Mhiri T.
Publication year - 2001
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/1097-4555(200101)32:1<33::aid-jrs663>3.0.co;2-p
Subject(s) - monoclinic crystal system , raman spectroscopy , hydroxyapatites , crystallography , chemistry , phase transition , phase (matter) , crystal structure , hexagonal phase , analytical chemistry (journal) , calcium , hexagonal crystal system , organic chemistry , quantum mechanics , optics , physics
In order to study the structure and dynamics of calcium–lead hydroxyapatites, Ca 10− x Pb x (PO 4 ) 6 (OH) 2 , the Raman spectra of Pb 10 (PO 4 ) 6 (OH) 2 and Ca 4 Pb 6 (PO 4 ) 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 Pb 10 (PO 4 ) 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. Ca 4 Pb 6 (PO 4 ) 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 PO 4 3− is also confirmed with Raman spectroscopy. Copyright © 2001 John Wiley & Sons, Ltd.