Crystalline structure modification of hydroxyapatite via a hydrothermal method using different modifiers

Abstract

In this study, hydroxyapatite (HAp) was synthesized using the hydrothermal method, where different modifiers, such as succinic acid, ascorbic acid, stearic acid, calcium phosphate, and silica, were used. The powdered HAp's morphological, compositional, and crystallographic features were explored using Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD) characterization techniques. Crystallographic characteristics, such as the lattice parameter, unit cell volume, and crystallinity degree, were calculated by utilizing XRD data. The crystallite size (<100 nm) was calculated using various models, including the Scherrer equation, the Sahadat–Scherrer model, the size-strain plot, the Halder–Wagner model, and different forms of Williamson–Hall plot. Williamson–Hall includes the uniform deformation model (UDM), the uniform stress deformation model (USDM), and the uniform deformation energy density model (UDEDM). Some models incorporate energy density, strain, and stress as additional components. The peaks at 962, 1026, and 1087 and 3000–3800 cm⁻¹ in FTIR absorption spectra indicated the presence of phosphate and hydroxide groups in the synthesized HAp. Additionally, the optical bandgap energy of the synthesized Hap was estimated to range from 5.29 eV to 5.60 eV. Rietveld refinement analysis revealed that HAp is the predominant phase, with tricalcium phosphate (TCP) generated alongside.