Type A–B carbonate chlorapatite synthesized at high pressure

Sodium-bearing type A–B carbonate chlorapatites {CCLAP; Ca10−(y+z)Nay□z[(PO4)6−(y+2z)(CO3)y+2z][Cl2−2x(CO3)x], with x≈y≈4z≈0.4} have been synthesized from carbonate-rich melts at 1350–1000 °C and 1.0 GPa, and investigated by single-crystal X-ray structure and FTIR spectroscopy. Typical crystal and compositional data are: a=9.5321(4) Å, c=6.8448(3) Å, space group P63/m, R=0.027, Rw=0.025, x=0.37(3), y=0.57(2). Crystal-chemical features and FTIR spectra are similar to Na-bearing type A–B carbonate hydroxyapatites (CHAP) and fluorapatites (CFAP) reported recently. The molar amounts of Na and channel (type A) carbonate maintain a near 1:1 ratio in all three composition series, confirming that the Na cation and A and B carbonate ion substituents exist as a defect cluster within the apatite matrix, to facilitate charge compensation and spatial accommodation. Uptake of carbonate is significantly lower in CCLAP than in CHAP for similar conditions of crystal synthesis.

Defect cluster (blue) of A carbonate ion in apatite channel, Na+ cation, and B carbonate ion replacing phosphate group, in carbonate chlorapatite synthesized at high pressure.Figure optionsDownload as PowerPoint slide