Hydroxyapatite nanoparticles synthesized with a wide range of Ca/P molar ratios and their structural, optical, and dielectric characterization

• Published in: Hanʼguk Seramik Hakhoe chi Vol. 59; no. 6; pp. 846 - 858
• Main Authors: Kashyap, Shreyas J., Sankannavar, Ravi, Madhu, G. M.
• Format: Journal Article
• Language: English
• Published: Singapore Springer Nature Singapore 01.11.2022
• Subjects: Ceramics; Chemistry and Materials Science; Composites; Glass; Materials Science; Natural Materials; Original Article; Ca/P molar ratio; Dielectric analysis; Hydroxyapatite; Rietveld refinement; TGA
• ISSN: 1229-7801; 2234-0491
• DOI: 10.1007/s43207-022-00225-w

Hydroxyapatite (HAp) nanomaterials have been synthesized via wet-chemical precipitation route with Ca/P molar ratios of 1.40, 1.60, 1.67, 1.80 and 2.00. These samples have been characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, Fourier transform-infrared spectroscopy (FT-IR), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRPD), Rietveld refinement and dielectric spectroscopy. Micrographs from SEM showed that the calcined HAp particles were spherical in shape and they were highly agglomerated. The chemical composition derived from EDX was in good accordance with the theoretical Ca/P ratio. FT-IR spectroscopy revealed the characteristic functional groups: PO 4 3− and OH − . Certain peaks were observed in the diffuse reflectance spectrum which is argued to originate from O 2− → Ca 2+ and O 2− → P 5+ charge transfer transitions. Phase analysis showed the existence of single pure HAp ( P 6 3 / m ) only for samples with Ca/P = 1.6 and 1.67. However, HAp with Ca/P = 1.4 had tricalcium phosphate (TCP, Ca 3 (PO 4 ) 2 ) as the secondary phase, while Ca/P = 1.8 and 2.0 had CaCO 3 as the secondary phase. Thermograms displayed multiple steps indicating the degradation of secondary phases at higher temperatures. Further, XRD analysis of post-TGA samples revealed that there was no change in the space group symmetry; however, the phase identified was Ca 5 (PO 4 ) 3 (CO 3 ) 0.01 (OH) 1.3 . The dielectric constant ( ε ′ ) and dielectric loss ( tan δ ) decline with enhancing frequency corresponding well with space-charge and ionic-type polarization behaviour. The ac electrical conductivity enhanced with increasing frequency obeying the Jonscher universal power law.