Formation energies of substitutional sodium and potassium in hydroxyapatite

Abstract

First-principles calculations are performed to investigate atomic and electronic structures of Na + and K + ions substituting for Ca 2+ in hydroxyapatite (HAp). Formation energies of the substitutional defects are obtained from total energies of defective HAp supercells and chemical potentials determined by assuming chemical equilibrium between HAp and HAp-saturated aqueous solution containing Na + or K +. It is found that substitutional Na + with a charge-compensating interstitial proton is more stably formed, as compared to substitutional K +. This may be related to the fact that Na + is generally more abundantly involved in bones and tooth enamels than K +. © 2009 The Japan Institute of Metals.