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The theoretical ferroelectric polarization of the low-temperature (monoclinic, P2 1 ) phase and the hightemperature (hexagonal, P6 3 ) phase of hydroxyapatite Ca 10 (PO 4 ) 6 (OH) 2 is calculated based on the density functional theory (DFT). In the monoclinic structure, the value of ferroelectric polarization is found to be 9.87 mC cm À2 along the [001] direction. In the hexagonal structure, the ferroelectric polarization is 7.05 mC cm À2 along the [001] direction. The main contribution to the electric polarization comes from ordered hydroxyl OH À anions for both phases, although the inorganic Ca 5 (PO 4 ) 3 apatite framework also gives a non-negligible contribution. A detailed analysis of ferroelectric polarization and structural change of the hydroxyapatite is presented for a better understanding of this important biomaterial.

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The thermodynamic stability of lanthanide cobaltites is also a function of their existing oxygen non-stoichiometry.

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of Perovskites in the lanthanumstrontium-manganese-iron oxide system, Journal of Solid State Chemistry, http://dx.Abstract The enthalpies of formation from binary oxides of perovskites (ABO 3 ) based on lanthanum strontium manganite La(Sr)MnO 3 (LSM) and lanthanum strontium ferrite La(Sr)FeO 3 (LSF) and mixed lanthanum strontium manganite ferrite La(Sr)Mn(Fe)O 3 (LSMF) were measured by high temperature oxide melt solution calorimetry. Using iodometric titration, the oxygen content was derived. The perovskites with A-site cation deficiency have greater oxygen deficiency than the corresponding A-site stoichiometric series. Stability of LSMF decreases with increasing iron content. Increasing oxygen deficiency clearly destabilizes the perovskites. The results suggest an enthalpy of oxygen incorporation that is approximately independent of composition.