Crystal Structure and Site Preference of Ba-Doped α-Tricalcium Phosphate (Ca1-xBax)3(PO4)2through High-Resolution Synchrotron Powder Diffraction (x= 0.05 to 0.15)

The single phase of barium-substituted alpha tricalcium phosphate (Ba-α-TCP) (Ca 1- x Ba x ) 3 (PO 4 ) 2 ( x = 0.05, 0.10, and 0.15) has been prepared by solid-state reactions. The crystal structure of the Ba-α-TCP powders has been investigated by high-resolution synchrotron powder diffraction and the Rietveld method. Diffraction data were successfully analyzed by the single phase Ba-α-TCP (space group P 2 1 / a ). Unit-cell parameters a, b, c, and β increase with increasing Ba content. Most of the Ba atoms are located at three crystallographic sites among the eighteen cation sites in the α-(Ca 1- x Ba x ) 3 (PO 4 ) 2 ( x = 0.05, 0.10, and 0.15). The refined positional parameters and occupancy factors of the preference sites for Ba substitutions were Ca17: (0.0909(6), 0.4167(2), 0.7823(5)) g (Ba) = 0.72(2); Ca11: (0.4068(6), 0.2506(2), 0.2199(5)) g (Ba) = 0.67(1); Ca5: (0.0983(6), 0.0837(2), 0.7857(5)) g (Ba) = 0.65(1) in the α-(Ca 0.85 Ba 0.15 ) 3 (PO 4 ) 2 . Here, g (Ba) is the occupancy factor of Ba atoms. These sites have relatively smaller bond valence sums, indicating the preference sites for the larger-sized Ba substitutions.