**4.10.3 Incorporation of 3d-metal ions to the hexagonal channel of apatite**

The compound having the formula: K3Ca2(SO4)3F, was identified in coatings of heat recovery cyclones of Portland clinker kiln. The structure of this phase (noncentrosymmetric, space

was reported as very distorted analogue of apatite where fluoride atoms are oriented along

**Fig. 35.** The structure of K3Ca2(SO4)3F according to FAYOS et al [212] phase in the perspective view along the c-axis.

D0 → <sup>7</sup>

The activation by Eu or Ce leads to the phosphor: K3Ca2(SO4)3F:Ce, Eu, which was prepared by PODDAR et al [213] via the precipitation method. The K3Ca2(SO4)3F:Ce luminescent pig‐ ment shows the emission at 334 nm when excited at 278 nm due to the 5*d*→4*f* transition of Ce3+ ions. The phases K3Ca2(SO4)3F:Eu2+ and K3Ca2(SO4)3F:Eu3+ show the emissions at 440 nm, and

F1 and 5

The synthesis, the characterization and ionic conductivity of Ca8−xSrxBi2(PO4)6O2 phase where *x* = 3, 4 and 5 was reported by TRABELSI et al [214]. Sr2+ ions were noted to occupy two sites (4*f*) and (6*h*), with a strong preference for (6*h*) sites. Heavy Bi3+ atoms preferentially occupied the

New bismuth calcium silicon oxide Ca4Bi4.3(SiO4)(HSiO4)5O0.95, with the apatite structure was synthesized by UVAROV et al [215]. The structure was refined from the powder X-ray diffrac‐ tion data. The refinement revealed that the phase had the P63/M space group with the unit cell

Also the structure of bismuth calcium vanadium oxide (BiCa4V3O13, BiCa4(VO4)3O) was reported by HUANG and SLEIGHT [216] as apatite without an inversion center. The phase crystallizes in hexagonal system with the space group P63, *a* = 9.819 Å, *b* = 7.033 Å, *V* = 587.2 Å3 and*Z* = 2. Calculated density is 4.129 g·cm−3. Lower symmetry ofthe structure may be related

D0 → <sup>7</sup>

and *c*:*a* = 0.734.

, *Z* = 4 and *ρ* = 2.61 g·cm−3)

F2 of Eu3+ ion, which are in blue and

group PN21A, *a* = 13.415, *b* = 10.943 and *c* = 9.127 Å, *V* = 1284.75 Å3

228 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

the pseudo-screw *a*-axis [211],[212].

596 and 615 nm via the transitions of 5

**4.10.2 Bismuth calcium oxyapatites**

(6*h*) site.

red region of the visible spectrum, respectively.

parameters *a* = 9.6090 Å, *c* = 7.0521 Å, *V* = 563.9 Å3

to the site selective distribution of Bi atoms at the Ca sites.

The hexagonal channel in the structure of apatite can accommodate infinite linear chains of [- Me-O-]n n−, where Me = Cu, Zn, Ni, Co… (**Fig. 36**). The incorporation of *3d-*metal ions in the hexagonal channels of strontium phosphate apatite (Sr5(PO4)3OH) was investigated by KAZIN et al [217].

**Fig. 36.** Crystal structure fragments of doped apatite showing the atomic arrangement at the hexagonal channel where 3-d metal atoms are located [217].

**Fig. 37.** Depiction of the structure in hexagonal channels (along the c-axis) in the lattice of copper-containing apatite: hydroxylapatite (a), hydroxylapatite with OH partially replaced by Cl and hydroxylapatite with OH partially replaced by F (c). The planes passing through Ca atoms depict the channel walls.

Doping of Sr5(PO4)3OH with ZnO, NiO and CoO at 1400°C in air resulted in the incorpora‐ tion of 3d-ions entering the hexagonal channels of the apatite structure, formally substitut‐ ing for protons in the OH groups. The structure of apatite channels in the phases with the composition of Sr5(PO4)3Zn0.15O0.3(OH)0.7 (white and shade of green), Sr5(PO4)3Ni0.2 O0.4(OH)0.6 (green) and Sr5(PO4)3Co0.2O0.5(OH)0.4 (dark-violet) contains O-Me-O fragments separated by OH groups. Co atoms were localized in the position shifted by 0.5 Å from the center of channel. Their coordination can be described as distorted from linear O-Co-O probably by additional coordination to phosphate oxygen atoms [217].

In other work of KAZIM et al [218], the synthesis and the properties of three compounds possessing the apatite structure with the composition of Ca5(PO4)3CuyOy+δ(OH)0.5−y−dX0.5, where the parameter *y* = 0.01 - 0.3 for *X* = OH, *y* = 0.01 − 0.1 for *X* = F and *y* = 0.1 for *X* = Cl. Similar copper containing vanadates Sr5(VO4)3CuO are formed as co-products in the synthesis of vanadium doped superconductors [218],[219].
