Characterization of Dicalcium Phosphate Anhydrous Crystals Synthesized by Using a Hydrothermal Process

Abstract

We report the synthesis and the characterization of dicalcium phosphate anhydrous (DCPA, CaHPO4) crystals prepared using a hydrothermal process. To prepare an aqueous solution containing Ca2+ and $$HPO_4^{2-}$$ ion precursors, we dissolved calcium nitrate tetrahydrate and ammonium phosphate dibasic, respectively, in deionized water at room temperature without adding a hydroxide precursor. The pH value was set to about 3.5. The structure and the morphology of the as-grown DCPA crystals were investigated using synchrotron X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy. Disk-shaped microcrystals with rectangular surfaces were observed. The (001) atomic planes of the triclinic monetite structure were aligned along the surface normal direction. We also found that the individual DCPA crystals were single crystals with well-aligned mosaic domains. The full width at half maximum of the φ-scan at off-specular (-1-12) Bragg peaks was approximately 0.061°. This indicated that the atomic positions of the DCPA crystals in the in-plane direction were highly ordered.