Crystallization, fluoridation and some properties of apatite thin films prepared through rf-sputtering from CaO–P2O5 glasses

Using calcium phosphate glass targets with the CaO/P2O5 molar ratios of 1.50–0.50, much lower than the stoichiometric value of 3.3 for hydroxyapatite, thin films of stoichiometric hydroxy-, nonstoichiometric oxyhydroxy- and Ca-deficient oxyhydroxy-apatites were prepared on alumina ceramic substrates by rf-sputtering followed by post-annealing. Based on the present results, a phase diagram for CaO–P2O5 at low temperatures in the ambience of air was depicted for thin films. The ambient H2O vapor had an influence on the phase diagram: Tricalcium phosphate was changed to apatite in the presence of H2O vapor. Dense fluorohydroxyapatite thin films were prepared by fluoridation of those apatite thin films at a low temperature such as 200°C. In the present report, some functional properties of thin films thus prepared were also shown.