Crystal Structure Analysis of Si‐ and Zn‐Codoped Tricalcium Phosphate by Neutron Powder Diffraction

Abstract

Tricalcium phosphate (TCP) is a candidate for a temporary bone implant. Attempts were made to tune the resorption rate of implant for bone reforming by doping different levels of Si and Zn. In this paper, the crystal structure of Si‐ and Zn‐codoped TCP (Si,Zn‐Ca3(PO4)2 (Si,Zn‐TCP)) was studied by using a time‐of‐flight neutron powder diffraction and the Rietveld analysis method. Si,Zn‐TCP was confirmed to have a rhombohedral structure (space group R3c, Z=21), with the unit cell parameters a=b=10.3958(1) Å, c=37.3122(7) Å, α=β=90°, and γ=120° in the hexagonal setting. Of the five cation sites, Ca(1), Ca(2), and Ca(3) positions are still occupied by Ca with minor change in Ca–O bond distance compared with the pure β‐TCP. Whereas the Ca(5) site was totally occupied by Zn. Compared with the original Ca(5)···O distance, the shorter and more uniform Zn(5)···O bond distances show the smaller cation substitution effect and a more ideal octahedral geometry. The site Ca(4) was partially substituted by Zn and Ca,Zn(4)···O(9) bond distance is 2.808(5) Å, much shorter than the original 3.041(1). The Zn substitution content is calculated to be 10% of total Ca sites. A fraction of Si substitutes for P(1) sites and the substitution content is calculated to be 3.9% of total phosphorus sites. The bond valence sums of Ca,Zn(4) is 0.97, higher than 0.67 for Ca(4) in β‐TCP. Other Ca and Zn(5) sites are close to 2.0.