Ferric iron in synthetic carbonate apatites: A Mössbauer effect study

Mayer, I.; Diab, H.; Felner, I.

doi:10.1016/0162-0134(92)80007-i

Cited by 16 publications

(15 citation statements)

References 6 publications

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“…Biogenic HAp differs from the synthetic compound due to the presence of foreign atomic (Mg 2+ , Na + , Cl − ) and molecular (CO 2− 3 , SiO 4− 4 ) ions. Although the role of most impurities is largely unknown, some studies suggest that the presence of a small concentration of iron (below 157 ppm) prevents the loss of calcium from bones and desorption of enamel from teeth [5,6]. Iron-doped HAp (Fe-HAp) has also attracted interest due to its intrinsic magnetic properties [7].…”

Section: Introductionmentioning

confidence: 99%

“…Interstitial iron (Fe i ) defects have been reported as well. Analysis of X-ray diffraction (XRD) data shows that iron can occupy 2b or 12i Wyckoff positions [5,[18][19][20]. The first site corresponds to the formation of a linear O-Fe-O structure in the center of the OH channel (site A at Figure 1), while the latter involves a three-fold coordinated Fe atom displacement towards the wall of the channel (site C at Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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Iron in Hydroxyapatite: Interstitial or Substitution Sites?

et al. 2021

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Iron-doped hydroxyapatite (Fe-HAp) is regarded as a promising magnetic material with innate biocompatibility. Despite the many studies reported in the literature, a detailed theoretical description of Fe inclusions is still missing. There is even no consensual view on what kind of Fe defects take place in Fe-HAp—iron interstitial or calcium substitutions? In order to address these questions, we employ modern first-principles methodologies, including hybrid density functional theory, to find the geometry, electronic, magnetic and thermodynamic properties of iron impurities in Fe-HAp. We consider a total of 26 defect configurations, including substitutional (phosphorus and calcium sites) and interstitial defects. Formation energies are estimated considering the boundaries of chemical potentials in stable hydroxyapatite. We show that the most probable defect configurations are: Fe3+ and Fe2+ substitutions of Ca(I) and Ca(II) sites under Ca-poor conditions. Conversely, Fe interstitials near the edge of the hydroxyl channel are favored in Ca-rich material. Substitutional Fe on the P site is also a probable defect, and unlike the other forms of Fe, it adopts a low-spin state. The analysis of Fe K-XANES spectra available in the literature shows that Fe-HAp usually contains iron in different configurations.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Iron in Hydroxyapatite: Interstitial or Substitution Sites?

et al. 2021

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“…3 The bonding characteristics in hydroxyapatite indicate that calcium ions occur in two nonequivalent lattice sites, four Ca 2+ along the 3-fold screw axis referred to as Ca 2+ (1) and another six situated symmetrically about the 6-fold screw axes referred to as Ca 2+ (2). 4 There are also two types of oxygens in the hydroxyapatite structure, namely, those comprising the phosphate tetrahedra and those bonded to the hydrogen atom (represented as O H ).…”

Section: Introductionmentioning

confidence: 99%

“…A single unit cell of HA consists of 44 atoms. Considering the different sites occupied by Ca and O in hydroxyapatite (as described above), the chemical formula can be rewritten as Ca (1) 4 Ca- (2) 6 Two stable phases are reported in literature for the crystal structure of hydroxyapatite. One phase corresponds to a P6 3 /m hexagonal symmetry, which is generally associated with nonstoichiometric HA containing F − or Cl − impurities.…”

Section: Introductionmentioning

confidence: 99%

Structural and Magnetic Phase Transformations of Hydroxyapatite-Magnetite Composites under Inert and Ambient Sintering Atmospheres

et al. 2015

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The present work reports the impact of sintering conditions on the phase stability in hydroxyapatite (HA)−magnetite (Fe 3 O 4 ) bulk composites, which were densified using either pressureless sintering in air or by rapid densification via hot pressing in inert atmosphere. In particular, the phase abundances, structural and magnetic properties of the (1−x)HA-xFe 3 O 4 (x = 5, 10, 20, and 40 wt %) composites were quantified by corroborating results obtained from Rietveld refinement of the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Mossbauer spectroscopy. Post heat treatment phase analysis revealed a major retention of Fe 3 O 4 in argon atmosphere, while it was partially/completely oxidized to hematite (α-Fe 2 O 3 ) in air. Mossbauer results suggest the hightemperature diffusion of Fe 3+ into hydroxyapatite lattice, leading to the formation of Fe-doped HA. A preferential occupancy of Fe 3+ at the Ca(1) and Ca(2) sites under hot-pressing and conventional sintering conditions, respectively, was observed. The lattice expansion in HA from Rietveld analysis correlated well with the amounts of Fe-doped HA determined from the Mossbauer spectra. Furthermore, hydroxyapatite in the monoliths and composites was delineated to exist in the monoclinic (P2 1 /b) structure as against the widely reported hexagonal (P6 3 /m) crystal lattice. The compositional similarity of iron doping in hydroxyapatite to that of tooth enamel and bone presents HA-Fe 3 O 4 composites as potential orthopedic and dental implant materials.

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“…Fe 3+ leads to unrealistic BVSs of 1.1 and 1.2 on the Ca F and Ca T sites, respectively. Many synthesis routes have been developed to incorporate Fe 3+ in HAp that have met with varying degrees of success in obtaining a single phase product[92][93][94][95][96][97]. Generally, the crystal chemistry was not considered in detail[98][99][100][101].…”

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confidence: 99%

The incorporation of small cations in hydroxyapatite : synthesis, crystal chemistry and functionality

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Hydroxyapatite (HAp) is an important oxide in biotechnology, and also holds promise as a heterogeneous catalyst. Its ideal composition is [(Ca F 4)(Ca T 6)(PO 4) 6 (OH) 2 ] where an adaptable framework (F) structure creates one-dimensional tunnels (T) that provide multiple ionic acceptor sites (Ca F /Ca T /P/OH) which can be adjusted to deliver specific functionality. Modification of cation and anion type and proportions, together with selection of appropriate syntheses, can be used to regulate structural distortions and phase transformations. However, first-principles crystallographic adaptation to optimize performance is less explored, especially for tailoring excipient responses and catalytic activity, which are the primary concern of this study. Bioactive and catalytic HAp is nanocrystalline and usually nonstoichiometric, especially with respect to cation vacancies, carbonate and water incorporation, and oxygen displacement of hydroxyl ions. The hypothesis explored in this thesis is that controlled doping of HAp by small cations (Fe 3+ , Zn 2+ , Mg 2+) will alter the crystal chemistry in a manner that enhances cell proliferation (biological application) and product yield (catalytic application). The selection of small cations for investigation was deduced from their abundance and essential role in bone metabolism and the potential of these metals for enhancing chemical conversion of alcohol while fixed in an environmentally benign HAp matrix. To this end, methods to synthesize homogeneous ceramic powders of single phase Fe-, Zn-, and Mg-HAps to the solid solubility limits of these metals were developed from which structure-property correlations were established. All three series were characterized with X-ray and neutron diffraction, electron microscopy, and several spectroscopies, including FTIR and NMR techniques, to corroborate crystallographic incorporation and concomitant symmetry transformations, determine phase proportions (crystalline and amorphous), and metal partitioning preferences across the Ca F /Ca T sites. Crystal structure refinement was challenging due to the fine-grain size, although in this physical form, large reactive surfaces are produced that are preferable for the targeted applications. It was found that the solid solution limit of Fe-HAps {nominally [(Ca 10-x Fe x)(PO 4) 6 (OH 2-x O x)]} was x = 0.5, with Fe 3+ entering the Ca F site at low loadings (x = 0.1) and subsequently residing in both the Ca F and Ca T at x = 0.5.

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Ferric iron in synthetic carbonate apatites: A Mössbauer effect study

Cited by 16 publications

References 6 publications

Iron in Hydroxyapatite: Interstitial or Substitution Sites?

Iron in Hydroxyapatite: Interstitial or Substitution Sites?

Structural and Magnetic Phase Transformations of Hydroxyapatite-Magnetite Composites under Inert and Ambient Sintering Atmospheres

The incorporation of small cations in hydroxyapatite : synthesis, crystal chemistry and functionality

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