DIELECTRIC-PROPERTIES AND STRUCTURE OF HYDROXYAPATITE CERAMICS SINTERED BY DIFFERENT CONDITIONS

Several conditions for hydroxyapatite ceramic preparation were used: s intering at 1150 degrees C in air or under H2O vapor flow, quenched in water at room temperature after sintering, or slow cooling inside the furnace. Depending on specific combinations of these preparation cond itions, in the resulting ceramics significant differences are observed in the phase composition and dielectric properties, ranging from capa citive to a semiconducting response. Comparison between the experiment al x-ray diffraction patterns and those calculated by the Rietveld met hod show that during sintering in air, approximately 40% of hydroxyapa tite is transformed to tricalcium phosphate. The XRD analysis shows th at this transformation could be possible using the following process: Ca-10(PO4)(6)(OH)(2) = 2Ca(3)(PO4)(2) + Ca2P2O7 + 2CaO + H2O.