Fully Dense Yttrium-Substituted Hydroxyapatite Coatings with Aligned Crystal Domains

Continuous yttrium-substituted hydroxyapatite (Y-HAP) coatings on titanium substrates were produced by an electrochemical/hydrothermal method. Hydroxyapatite seeds were first deposited on the titanium surface by electrochemical deposition. Subsequent hydrothermal crystal growth of Y-HAP onto the seed layer was investigated over a range of experimental conditions. Under certain conditions, it was discovered that well-crystallized and fully dense Y-HAP films were produced consisting of crystal domains oriented with the crystallographic c-axis normal to the substrate. At elevated temperatures, protons conduct along the c-axis of Y-HAP crystals. The novel film microstructure can therefore potentially be exploited in new applications of Y-HAP in bioelectrets, fuel cells, and electrochemical sensors.