Iron in Hydroxyapatite: Interstitial or Substitution Sites?

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 pl...

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Autores principales:	Leon Avakyan, Ekaterina Paramonova, Vladimir Bystrov, José Coutinho, Sandrine Gomes, Guillaume Renaudin
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	iron doping hydroxyapatite bioceramics density functional theory hybrid density functional X-ray absorption spectroscopy Chemistry QD1-999
Acceso en línea:	https://doaj.org/article/87918facf00642a4b4791fe0e5096867
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spelling	oai:doaj.org-article:87918facf00642a4b4791fe0e50968672021-11-25T18:31:22ZIron in Hydroxyapatite: Interstitial or Substitution Sites?10.3390/nano111129782079-4991https://doaj.org/article/87918facf00642a4b4791fe0e50968672021-11-01T00:00:00Zhttps://www.mdpi.com/2079-4991/11/11/2978https://doaj.org/toc/2079-4991Iron-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: Fe<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mrow><mn>3</mn><mo>+</mo></mrow></msup></semantics></math></inline-formula> and Fe<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></semantics></math></inline-formula> 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.Leon AvakyanEkaterina ParamonovaVladimir BystrovJosé CoutinhoSandrine GomesGuillaume RenaudinMDPI AGarticleiron dopinghydroxyapatite bioceramicsdensity functional theoryhybrid density functionalX-ray absorption spectroscopyChemistryQD1-999ENNanomaterials, Vol 11, Iss 2978, p 2978 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	iron doping hydroxyapatite bioceramics density functional theory hybrid density functional X-ray absorption spectroscopy Chemistry QD1-999
spellingShingle	iron doping hydroxyapatite bioceramics density functional theory hybrid density functional X-ray absorption spectroscopy Chemistry QD1-999 Leon Avakyan Ekaterina Paramonova Vladimir Bystrov José Coutinho Sandrine Gomes Guillaume Renaudin Iron in Hydroxyapatite: Interstitial or Substitution Sites?
description	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: Fe<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mrow><mn>3</mn><mo>+</mo></mrow></msup></semantics></math></inline-formula> and Fe<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></semantics></math></inline-formula> 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.
format	article
author	Leon Avakyan Ekaterina Paramonova Vladimir Bystrov José Coutinho Sandrine Gomes Guillaume Renaudin
author_facet	Leon Avakyan Ekaterina Paramonova Vladimir Bystrov José Coutinho Sandrine Gomes Guillaume Renaudin
author_sort	Leon Avakyan
title	Iron in Hydroxyapatite: Interstitial or Substitution Sites?
title_short	Iron in Hydroxyapatite: Interstitial or Substitution Sites?
title_full	Iron in Hydroxyapatite: Interstitial or Substitution Sites?
title_fullStr	Iron in Hydroxyapatite: Interstitial or Substitution Sites?
title_full_unstemmed	Iron in Hydroxyapatite: Interstitial or Substitution Sites?
title_sort	iron in hydroxyapatite: interstitial or substitution sites?
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/87918facf00642a4b4791fe0e5096867
work_keys_str_mv	AT leonavakyan ironinhydroxyapatiteinterstitialorsubstitutionsites AT ekaterinaparamonova ironinhydroxyapatiteinterstitialorsubstitutionsites AT vladimirbystrov ironinhydroxyapatiteinterstitialorsubstitutionsites AT josecoutinho ironinhydroxyapatiteinterstitialorsubstitutionsites AT sandrinegomes ironinhydroxyapatiteinterstitialorsubstitutionsites AT guillaumerenaudin ironinhydroxyapatiteinterstitialorsubstitutionsites
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Iron in Hydroxyapatite: Interstitial or Substitution Sites?

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