Determination of precise unit-cell parameters of the alpha-tricalcium phosphate Ca-3(PO4)(2) through high-resolution synchrotron powder diffraction

Unit-cell parameters of the alpha-tricalcium phosphate [TCP; Ca-3(PO4)(2)] were investigated using high-resolution synchrotron powder diffraction and the Rietveld method. The diffraction experiment was conducted at 29 degrees C at the BL-15XU experimental station of SPring-8, Japan. Precise unit-cell parameters of the alpha-TCP were obtained; a=12.87271 (9), b=27.28034(8), c=15.21275(12) angstrom, alpha=gamma=90 degrees, and beta=126.2078(4)degrees. The calculated density of alpha-TCP (2.8677 g/cm(3)) is smaller than that of beta-TCP, indicating the looser structure of alpha-TCP.