Cosubstitution of Zinc and Strontium in β-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 β‐tricalcium phosphate (β‐TCP), a well‐known resorbable biomaterial. The formation Zn2+ and Sr2+ cosubstituted β‐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 β‐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 β‐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 β‐TCP occurred at 800°C and well crystalline β‐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 β‐TCP. Zn2+ prefers to occupy the sixfold coordinated Ca (5) site whereas Sr2+ preferentially occupies the ninefold coordinated Ca (4) site of β‐TCP structure.