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RESEARCH PRODUCT

The influence of Fe3+ doping on thermally induced crystallization and phase evolution of amorphous calcium phosphate

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The present study investigates thermally induced crystallization and phase evolution of amorphous calcium phosphate (ACP) partially substituted with Fe3+ ions (M/P = 1.5 : 1). It was demonstrated that the presence of Fe3+ ions radically changes the crystallization behavior of ACP and completely prevents the formation of α-tricalcium phosphate (α-TCP, Ca3(PO4)2), which is the first crystalline phase obtained from non-substituted ACP upon thermal treatment. Surprisingly, calcium deficient hydroxyapatite (CDHA) was obtained instead of α-TCP. Such unusual crystallization behavior was observed with a doping level as low as 0.1 mol% with respect to Ca ions. Moreover, it was shown that the presence of Fe3+ ions significantly reduces the crystallization temperature of ACP, which started already at around 400 °C, whereas pristine ACP crystallizes to α-TCP only at around 600 °C. In the presence of Fe3+ ions β-TCP was also obtained at reduced temperature, compared to the formation from non-substituted ACP. The temperature of the complete conversion of CDHA to β-TCP was found to be dependent on the concentration of Fe3+ ions. The crystallization process and phase evolution were monitored employing thermal analysis, XRD, FTIR, Raman, EPR and Mossbauer spectroscopies.