Mayora Varshney
School of Applied and Life Sciences, University Institute of Technology, Uttaranchal University, Dehradun, 248007, Uttarakhand, India.

Aditya Sharma
Department of Physics, University of Petroleum and Energy Studies, Dehradun, 248007, Uttarakhand, India.

B. H. Lee
Advanced Analysis Centre, Korea Institute of Science and Technology, Seoul, 02792, South Korea.

Sung Ok Won
Advanced Analysis Centre, Korea Institute of Science and Technology, Seoul, 02792, South Korea.

DOI https://doi.org/10.33889/PMSL.2026.5.1.008

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Abstract

The synthesis of bio-relevant calcium phosphates has attracted considerable attention, as even minor deviations in the stoichiometric Ca/P ratio (1.5 ≤ Ca/P ≤ 1.67) can induce the formation of multiple crystalline phases. In this study, the combined influence of nominal Ca/P ratio and synthesis temperature on the phase evolution of calcium phosphates was systematically investigated. Calcium phosphate powders with Ca/P ratios of 1.4, 1.5, 1.6, and 1.67 were synthesized over a wide temperature range, from ice-bath conditions to 200°C, followed by calcination at 800°C, while maintaining a constant pH of 10 for all samples. Regardless of the synthesis temperature and Ca/P ratio, calcium-deficient hydroxyapatite (CDHA) was initially precipitated. For nominal Ca/P ratios of 1.4 and 1.5, CDHA synthesized under ice-bath conditions transformed into β-tricalcium phosphate (β-TCP) after calcination. Samples with Ca/P = 1.6 exhibited mixed phases of hydroxyapatite (HA) and β/α-TCP upon calcination, independent of synthesis temperature. In contrast, HA was obtained after calcination of CDHA samples synthesized at temperatures ≥50°C with a Ca/P ratio of 1.67. The observed phase diversity is rationalized in terms of temperature-dependent Ca²⁺ ion migration at the molecular level, governing compositional homogeneity and phase stability.

Keywords- Ca/P ratio, Calcium-deficient hydroxyapatite (CDHA), β-TCP, Ice bath.

Citation

Varshney, M., Sharma, A., Lee, B. H., & Won, S. O (2026). Growth Behavior of Nano-Hydroxyapatite as Affected by Synthesis Temperature and Ca/P Ratio of Precursors. Prabha Materials Science Letters, (1), 159-173. https://doi.org/10.33889/PMSL.2026.5.1.008.