title: The effect of chemical potential on the thermodynamic stability of carbonate ions in hydroxyapatite.
abstract: First-principles calculations were performed for CO3(2-) ions in hydroxyapatite in order to investigate the atomic structures and thermodynamic stability of CO3(2-) and its related defects. Two different chemical equilibrium conditions in high-temperature and aqueous-solution environments were considered, and atomic and ionic chemical potentials for the individual chemical equilibrium conditions were evaluated to calculate defect formation energies. It was found that A-type CO3(2-) (substituting OH(-)) is energetically more favorable than B-type CO3(2-) (substituting PO4(3-)) in the high-temperature environment, whereas B-type is preferred to A-type in the aqueous solution environment. This result successfully reproduces experimentally observed trends. In the formation of A-type and B-type CO3(2-), OH(-) vacancies or protons (interstitial or substitutional) act as charge-compensating defects.
authors.affiliation: Department of Materials Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Aichi, Japan.
authors.forename: Tomonori
authors.initials: T
authors.lastname: Kubota
authors.affiliation: Department of Materials Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Aichi, Japan.
authors.forename: Atsutomo
authors.initials: A
authors.lastname: Nakamura
authors.affiliation: Department of Materials Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Aichi, Japan.
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Toyoura
authors.affiliation: Department of Materials Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Aichi, Japan; Nanostructures Research Laboratory, Japan Fine Ceramics Center, 2-4-1, Mutsuno, Atsuta-ku, Nagoya 456-8587, Aichi, Japan. Electronic address: kmatsunaga@numse.nagoya-u.ac.jp.
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Matsunaga
mesh_terms: D001031:Apatites / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry*; D002254:Carbonates / Q000737:chemistry*; D003198:Computer Simulation; D004355:Drug Stability; D017886:Durapatite / Q000737:chemistry*; D008422:Materials Testing; D008956:Models, Chemical; D008958:Models, Molecular; D013816:Thermodynamics
chemical_list: D001031:Apatites; D001672:Biocompatible Materials; D002254:Carbonates; C030782:carboapatite; D017886:Durapatite
keywords: Carbonate ion; Defect formation energy; First-principles calculation; Hydroxyapatite; Thermodynamic stability