Fluorine-chlorine interaction in fluor-chlorapatite

Compressibility of carbonophosphate bradleyite Na3Mg(CO3)(PO4) by X-ray diffraction and Raman spectroscopy

“…This kind of structure allows a certain amount of substitution of [CO 3 ] 2− for [PO 4 ] 3− and Na + for Ca 2+ , generally adjusting the types and proportions of additional anions to maintain neutral. The transition from apatite (fluorapatite) phase to bradleyite framework has been proposed to be realized because the transformation between hexagonal and monoclinic based on substitution has been evidenced in calcium phosphate minerals, with the atomic positions being similar in two symmetries (Hughes et al 1990;Mackie and Young 1974).…”

Raman spectroscopy, 19F and 31P MAS-NMR of a series of fluorochloroapatites

“…Previous diffraction studies 14,15 have show that interactions between F − and Cl − results in complex structural features in binary fluorochloroapatites compared to the pure end members. 15 Structural anomalies were attributed to: (i) a trimodal distribution of fluorine sites; in addition to the expected position of fluorine at the centre of the calcium-triads, fluorine is also displaced around 0.2 and 0.6 Å from this position in the c-axis ion channels, (ii) an excess of halogen ions per unit cell compared to the stoichiometric total of two and (iii) initial stabilisation of the chlorapatite monoclinic structure with fluorine addition, which destabilised to hexagonal on higher F − incorporation.…”

“…11 However, the larger chlorine ion (181 pm compared to 133 pm for fluorine 12 ) substitutes in a disordered fashion onto the 0 and 1/2 positions. Pure chlorapatite exhibits a monoclinic structure: P2 1 /b, [13][14][15] however in binary and ternary compounds such as Ca 5 (PO 4 ) 3 (F, Cl) and Ca 5 (PO 4 ) 3 (F,Cl,OH) both monoclinic and hexagonal structures have been observed. 16 It has been noted that this large anion shift 0955 in chlorapatite compared to fluorapatite in the tunnels along the 6 3 screw axis with no change in the calcium triad positions possibly limits solid solution behaviour in this system.…”

The effect of type-B carbonate content on the elasticity of fluorapatite

“…The chemical formulae of CFAP samples, obtained from electron microprobe analysis (Table 2) and FTIR spectra, indicate the presence of carbonate in both samples and show an excess of F. In their analysis of fluor-chlorapatite, Mackie and Young (1974) noted (F + Cl) > 2 halogen atoms per formula unit (apfu) for their two samples, both by chemical analysis (2.06, 2.25 halogen apfu for two samples) and by X-ray site refinement (2.09, 2.19 apfu). They proposed the presence of an additional Cl site at (0,0,0) that they could not asses from their results.…”