Experimental Visualization of Chemical Bonding and Structural Disorder in Hydroxyapatite through Charge and Nuclear-Density Analysis

Yashima, Masatomo; Yonehara, Yukihiko; Fujimori, Hirotaka

doi:10.1021/jp208746y

Cited by 49 publications

(56 citation statements)

References 37 publications

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“…We have explored the influence of the supercell size on the formation energies of defects and HAp structural parameters. Unit-cell and initial 100 positional parameters for HAp were taken from [24]. Extensive convergence test defined the energy cutoffs of 40 Ry for the smooth part of the electron wave functions and 320 Ry for the augmented electron density.…”

Section: Density Functional Theory Based Calculationsmentioning

confidence: 99%

Nitrogen-containing species in the structure of the synthesized nano-hydroxyapatite

et al. 2014

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Synthesized by the wet chemical precipitation technique hydroxyapatite powders (HAp) with the sizes of the crystallites of (20-10 50) nm and 1 m were analyzed by multi-frequency (9 and 95 GHz) electron paramagnetic resonance (EPR) methods. It is shown that during the synthesis process nitrate anions from the reagents (by-products) could incorporate into the HAp structure. The relaxation times and EPR parameters of the axially symmetric NO 3 2paramagnetic centers detected after X-ray irradiation of the product at room temperature are measured with high accuracy. Assignments of the observed EPR spectra as compared with that given in literature are discussed. Analyses of electron-nuclear double resonance (ENDOR) data from 1 H and 31 P nuclei and ab-15 initio density functional theory (DFT) calculations allow suggesting that the paramagnetic centers and nitrate anions as the precursors of NO 3 2radicals preferably occupy PO 4 3site in the HAp structure. 65 110 Troullier-Martins pseudopotentials [27] with the plane-wave cutoff energy of 70 Ry.

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Section: Density Functional Theory Based Calculationsmentioning

confidence: 99%

Nitrogen-containing species in the structure of the synthesized nano-hydroxyapatite

et al. 2014

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“…The O-H and P-O bond lengths are 0.978 A and 1.535 A, which match well with the measurement (0.971 A and 1.540 A), respectively. 10 The nine constructed HAp surfaces (SF1-9) were optimized and presented in Fig. S3.…”

Section: Resultsmentioning

confidence: 99%

“…The surface-dependent protein adsorption, cellular adhesion and biomineralization of HAp have great impact on the bone growth and repair processes. 6,7 Thus, many studies [8][9][10][11][12][13][14][15][16][17][18] have been devoted to the HAp surface structure including its morphology, surface energy, charge, crystallinity and stoichiometry. Using nuclear magnetic resonance NMR spectroscopy, Jager et al 13 and Osman et al 14 explored the surface structure of HAp nanocrystals and found that neither composition nor structure in the surface layer is same as that in the bulk crystal.…”

Section: Introductionmentioning

confidence: 99%

Probing the surface structure of hydroxyapatite through its interaction with hydroxyl: a first-principles study

et al. 2018

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Understanding the interaction of the hydroxyapatite (HAp) surface with hydroxyl originating from either the alkalescent physiological environment or HAp itself is crucial for the development of HAp-based biomaterials. Periodical density functional theory calculations were carried out in this study to explore the interaction of the HAp (100), (010) and (001) facets with hydroxyl. Based on a comparison study of Ca-rich, PO 4 -rich and Ca-PO 4 -OH mixed surfaces, the interaction pattern, interaction energy and effect of an additional water molecule on the Ca-OH interaction were comprehensively studied. The formation of CaOH on the Ca-rich surface was energetically favored on (100) and (001), while Ca(OH) 2 was energetically favored on (010). The Ca-water interaction was competitive, but had lower interaction energy than Ca-OH. Furthermore, Ca-O bonding and its influence on the OH stretching vibration were analyzed. Our calculations suggest that the hydroxyl-coated surface structure is more appropriate than the commonly used Ca-terminated surface model for studying HAp surface activity in its service environments.

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“…Therefore, Cr-Ap can be represented by Ca 5 (CrO 4 ) 3 (O, OH) 0.7 , where O 2e sites are partially occupied by both O 2− and OH − ions as is the case with typical hydroxy-apatite phases. 10 Figure 2 shows electrical conductivity σ of Cr-Ap as a function of oxygen partial pressure p O2 at elevated temperatures. Based on the Ca-Cr-O ternary phase diagram reported by Adendorff et al, 12 the apatite phase is stable in a narrow temperature region from about 780 to 900 • C under ambient atmosphere.…”

Section: Resultsmentioning

confidence: 99%

Mixed Proton Electron Conductivity of Calcium Chromate(V) Apatite

Aoki

Kikutani

Tsuji

et al. 2014

ECS Electrochemistry Letters

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This is the first report to investigate on the electrical conductivity of unusual high valence state pentavalent chromium oxides in terms of defect thermodynamics. Calcium chromium(V) apatite was prepared as a single phase, and the electrical conductivity was examined as a function of oxygen partial pressure p O2 . The conductivity was increased at higher p O2 in wet atmosphere but it was not dependent on p O2 in dry atmosphere. The water concentration cell gives stable electromotive force. The features disclosed that the chromium(V) apatite reveals proton electron mixed conductivity under wet oxidative condition.The apatite is a group of rare earth or alkaline earth salts of tetrahedral MO 4 oxoanions (M = P 5+ , Si 4+ , Ge 4+ , As 5+ etc.). Early studies have revealed that there are many interesting characteristics in these materials. The most important one, however, is their oxide ionic conductivity. Apatite oxide ion conductors (rare earth silicates) were first found by Nakayama et al. in 1995. 1,2 They show fairly high oxide ionic conductivity in an intermediate temperature range of 500-800 • C. 3 In addition, they have ionic transport numbers which are very close to 1.0 with a wide oxygen partial pressure range, 4 thus being considered as candidates for intermediate temperature solid oxide fuel cell (IT-SOFC) electrolytes.Typical apatite-type oxides tend to be electronically insulator because of the nature of the constituent cations with closedshell configuration. Meanwhile, apatite-type calcium chromate(V), Ca 5 (CrO 4 ) 3 (OH), comprising from Cr V O 4 3− oxoanions are reported to reveal semiconductor characteristics at elevated temperature because of the mobile electrons derived from d 1 configuration Cr V ions. 5 Hence, it is reasonably expected that this compound retains superimposed electronic conduction and ionic conductivity at intermediate temperatures. Such a material is promising for the cathode/anode materials of fuel cells, gas separation membranes and so on. 6,7 In this study, we investigate on the electrical conduction behavior of apatitetype calcium chromate(V) under various oxygen partial pressure in order to explore the feasibility of mixed ion electron conductivity in apatite phase. ExperimentalApatite-type calcium chromate was prepared by thermal decomposition of Ca II -Cr VI mixed precursors. 8,9 Ca(CH 3 COO) 2 (99.9% purity, Kanto) and CrO 3 (99.9% purity, Kanto) powders were dissolved into Milli-Q water at a stoichiometric Ca/Cr molar ratio. The solution were heated at 140 • C in order to evaporate water and thus, the Ca(II)-Cr(VI) mixed precursor powders were obtained. The precursors were once heated at 500 • C for 1 h in air and then annealed at 860 • C for 6 h in air and quenched at room temperature. Finally, the products were annealed at 930 • C in a wet Ar atmosphere (p H2O = 3 kPa) prepared by bubbling in water at 25 • C, giving desired apatite compound. The dark green powder thus obtained was examined by X-ray diffractometry (XRD) to check the phase purity. Scanning electron m...

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Experimental Visualization of Chemical Bonding and Structural Disorder in Hydroxyapatite through Charge and Nuclear-Density Analysis

Cited by 49 publications

References 37 publications

Nitrogen-containing species in the structure of the synthesized nano-hydroxyapatite

Nitrogen-containing species in the structure of the synthesized nano-hydroxyapatite

Probing the surface structure of hydroxyapatite through its interaction with hydroxyl: a first-principles study

Mixed Proton Electron Conductivity of Calcium Chromate(V) Apatite

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