Energetics of Sn2+ isomorphic substitution into hydroxylapatite: first-principles predictions

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The energetics of Sn2+ substitution into the Ca2+ sublattice of hydroxylapatite (HA), Ca10(PO4)6(OH)2, has been investigated within the framework of density functional theory. Calculations reveal that Sn2+ incorporation via coupled substitutions at Ca(ii) sites is energetically favourable up to a composition of Sn6Ca4(PO4)6(OH)2, and further substitutions at Ca(i) sites proceed once full occupancy of Ca(ii) sites by Sn2+ is achieved. Compositions of SnxCa10−x(PO4)6(OH)2 (x = 4-9) are predominant, with an optimal stoichiometry of Sn8Ca2(PO4)6(OH)2, and Sn-substituted HA follows approximately Vegard's law across the entire composition range. © The Royal Society of Chemistry.

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