Cosubstitution of Zinc and Strontium in -Tricalcium Phosphate: Synthesis and Characterization
The present study aimed at investigating the cosubstitution of two biologically important cations, namely Zn2+ and Sr2+, in the structure of -tricalcium phosphate (-TCP), a well-known resorbable biomaterial. The formation Zn2+ and Sr2+ cosubstituted -Ca3(PO4)2 has been ensured through aqueous coprecipitation technique that involves the addition of Zn2+ and Sr2+ containing precursors to partially replace Ca2+ in a calcium-deficient apatite composition during the synthesis, followed by heat treating the resultant apatites at 800°C to form single-phase -Ca3(PO4)2. Five different concentrations of single or combined substitution of elements have been investigated and the results were compared with those of pure -TCP without any substituted Zn2+ and Sr2+. The obtained materials were characterized by X-ray diffraction, FT-IR, elemental analysis, and Rietveld refinement techniques. The transformation of deficient apatites to Zn2+ and Sr2+ cosubstituted -TCP occurred at 800°C and well crystalline -TCP materials were formed at 1000°C with the typical rhombohedral structure at hexagonal setting (space group R3c). The Rietveld refinement results revealed gradual decreases in the a-axis and c-axis lattice parameters with increasing concentration levels of Zn2+ and Sr2+ substituted in the lattice of -TCP. Zn2+ prefers to occupy the sixfold coordinated Ca (5) site whereas Sr2+ preferentially occupies the ninefold coordinated Ca (4) site of -TCP structure.
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