Piezoelectricity in the Ordered Monoclinic Hydroxyapatite

The results are based on the first principle modeling and calculations of hydroxyapatite (HAP) nanostructures, especially, in ordered monoclinic phase. HAP structures were studied using local density approximation (LDA) method with calculations of density of states (DOS) in combination with molecular modeling by HyperChem. Computed data show that monoclinic and hexagonal phases can co-exist, especially in their ordered (along OH groups) states. Calculated piezoelectric coefficient dyy ∼ d33 ∼ 15.7 pm/V is consistent with recently obtained experimental data (effective longitudinal piezoelectric coefficient d33eff about 8 pm/V), which vary significantly from grain to grain and may correspond to coexisting phases.