Phase Composition of Sputtered Film from a Mixture Target of Hydroxyapatite and Strontium-apatite

To obtain an Sr-substituted hydroxyapatite thin film, sputter-coating was performed on a cellulose filter acting as a substrate from the mixture target of hydroxyapatite (HA) and strontium-apatite (SrAp) at an Ar pressure of 0.5-5.0 Pa. The ratio of the SrAp in the mixture target was varied from 25% to 100%. After coating, the films were heated at 700 °C to remove the cellulose filter substrate, and the crystalline phases were identified by X-ray diffraction (XRD). The sputter-coated film was identified as the Sr-substituted β-tri-calcium phosphate (TCP) and the Sr-substituted β-calcium pyrophosphate (CPP) as well as the Sr-substituted HA. The weight ratio of the Sr-substituted HA decreased with increasing Ar pressure or with an increasing ratio of SrAp to HA in the target. The average Sr/(Ca + Sr) molar ratio in the film was 1.9%-3.5% slightly lower than the initial SrAp ratio of the target, and the ratio was not influenced by the Ar pressure. In the (Sr + Ca)/P ratio, the ratio decreased while increasing the SrAp ratio in the target.