Water-based sol–gel synthesis and crystal structure refinement of lanthanum silicate apatite

A novel synthesis method of lanthanum silicate apatite was developed by a sol–gel method using an aqueous solution system. The processes of apatite phase formation were investigated by X-ray diffraction (XRD) analysis and thermogravimetric/differential thermal analyses (TG–DTA) using a precursor and heat-treated samples between 873 K and 1773 K. Crystal structure refinement of the sample heat-treated at 1773 K was carried out by using XRD and high resolution neutron powder diffraction profiles. Based on the combined results of XRD and TG–DTA, lanthanum dioxide carbonate (La2O2CO3) was found to be contained in the sample heat-treated below 873 K. Lanthanum silicate apatite was formed above 1073 K, a temperature that was in good agreement with the decomposition temperature of La2O2CO3. Furthermore, it was found that the profiles of powder XRD and high resolution neutron powder diffraction could be refined by the oxy-apatite structure with the space group P63/m (No. 176).