**6.3.4. Metaborate ion-containing apatite phase**

constituted a symmetric vibrator with a stretching vibration active in Raman spectrometry.

The final product was a solid solution of hydroxyl- and peroxide-apatite. However, the existence of peroxide ions in the HA lattice caused the contraction of the unit-cell dimen‐ sions of HA materials. In addition, a new hydrogen bond was formed between peroxide ions and adjacent OH radicals, which was determined by using molecular spectroscopy analysis. During annealing treatment in air, peroxide ions decomposed and the substituted OH radicals re-entered the HA lattice, resulting in the elimination of the structural aberrations caused by the incorporation of peroxide ions. The concentration of peroxide ions present in HA sam‐

2−-containing HA samples.

[87] phosphate apatitic phases of

(**Fig. 14**(**a**));

(**Fig. 14** (**b**));

(**Fig. 14**(**c**));

(**Fig. 14** (**d**)).

This vibration was recorded at 750 cm−1 in the Raman spectra of O2

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

ples was measured by chemical analysis [86].

The synthesis and the structure of four new chalcogenide5

**1.** Ca10(PO4)6S: *a* = 9.4619 Å, *c* = 9.8342 Å, *c*:*a* = 0.7223 and *V* = 529.88 Å<sup>3</sup>

**2.** Sr10(PO4)6S: *a* = 9.8077 Å, *c* = 9.2089 Å, *c*:*a* = 0.7350 and *V* = 600.53 Å<sup>3</sup>

**3.** Ba10(PO4)6S: *a* = 10.2520 Å, *c* = 7.6590 Å, *c*:*a* = 0.7471 and *V* = 697.14 Å<sup>3</sup>

**4.** Ca10(PO4)6Se: *a* = 9.5007 Å, *c* = 9.8406 Å, *c*:*a* = 0.7200 and *V* = 534.73 Å<sup>3</sup>

 The elements from the chalcogenide group (or oxygen group family) belonging to Group 16 (VI A) of the periodic table: O, S, Se, Te and Po. Elements sulfur, selenium and tellurium are also termed as the elements from the sulfur subgroup [87].

**6.3.3. Chalcogenide phosphate apatites**

the composition given by the formula:

were reported by HENNING et al [88].

5

Strontium borate-phosphate Sr10(PO4)5.5(BO4)0.5(BO2) 6 was prepared from SrCO3, NH4H2PO4 and H3BO3 at high temperature (from 1150 to 1550°C) and was found to be free of alkali metal compounds. Sr10(PO4)5.5(BO4)0.5(BO2) phase is a derivative of the apatite crystal structure with metaborate ion at Z-site: space group P3, *a* = 9.7973 Å, *c* = 7.3056 Å, *V* = 607.29 Å3 , *Z* = 1 [89],[90], [91].

The strontium sites are found to be fully occupied, while [PO4] 3¯ tetrahedra are partially replaced by [BO4] 5¯ groups. The crystal structure contains Sr cations occupying the 6*g* (Sr(1)) and 2*d* (Sr(2), Sr(3)) sites, isolated tetrahedral [PO4] 3¯/[BO4] 5¯ groups and linear [BO2]¯ groups located in hexagonally shaped (trigonal antiprismatic) channels formed by Sr(1) atoms and running along [001] (**Fig. 15**). The space group of the present compound is reduced to P3, because the orientation of the [PO4]/[BO4] tetrahedra destroys the mirror plane characteristic for the apatite crystal structure (P63/M) [89],[91].

**Fig. 15.** Crystal structure of Sr10(PO4)5.5(BO4)0.5(BO2): projection along [001] showing the hexagonally shaped channels formed by Sr(1) around the threefold inversion axis (Z = (P0.95B0.05) (a) and side view emphasizing the linear [BO2] − groups and the corresponding trigonal antiprisma formed by Sr(1) (b) [89].

<sup>6</sup> See also **Section 5.3.**
