title: Softening of hydroxyapatite by vacancies: a first principles investigation.
abstract: First-principles plane-wave calculations were performed to investigate the influences of intrinsic vacancy on the stability and elastic properties of hydroxyapatite (HA). Five types of vacancies, i.e. H, O, OH, Ca, and Ca(2+) vacancy, were considered. Formation energies were evaluated and compared with experimental measurements. It was shown that HA with a Ca(2+) vacancy is the most stable one among the considered systems. Elastic constants were estimated via curves of total energy against strain. Bulk, shear and Young's moduli, and Poisson's ratio are also evaluated to compare with the experimental value. The elastic properties of HA are significantly affected by the vacancy. Vacancy can soften HA via reducing its elastic moduli. The HA with Ca(2+) vacancy is the softest one among the considered systems. Electronic structures of HA with vacancy are also analyzed to explain the softening mechanisms.
authors.affiliation: School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, 2 West Wenhua Road, Weihai 264209, China.
authors.forename: J P
authors.initials: JP
authors.lastname: Sun
authors.forename: Y
authors.initials: Y
authors.lastname: Song
authors.forename: G W
authors.initials: GW
authors.lastname: Wen
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: R
authors.initials: R
authors.lastname: Yang
mesh_terms: D002118:Calcium / Q000737:chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray; D017886:Durapatite / Q000737:chemistry*; D055119:Elastic Modulus; D004583:Electrons; D013816:Thermodynamics
chemical_list: D017886:Durapatite; D002118:Calcium
keywords: Elastic properties; First-principles; Hydroxyapatite; Vacancy