Phase relations between β-tricalcium phosphate and hydroxyapatite with manganese(II):: Structural and spectroscopic properties

The preparation of Mn-containing beta-tricalcium phosphate (beta-TCP) samples was achieved in two ways: a) transformation of precipitated Mn-containing calcium hydroxyapatite (HA) to beta-TCP by heating at 1100 degrees C, and b) preparation by solid-state reaction of a mixture of CaCO3, (NH4)(2)HPO4, and Mn(NO3)(2) at 1100 degrees C. Powder X-ray diffraction (XRD) analyses of the samples, obtained by both methods, show well-defined patterns with structural data of the rhombohedral R3c, beta-TCP phase. The calculated lattice constants are smaller than those known for beta-Ca-3(PO4)(2) because of substitution of Ca2+ by Mn2+. EPR spectroscopy indeed reveals that manganese is divalent in the samples. Apparently, the Ca(5) site in the beta-TCP structure is occupied by Mn2+. The distribution of Mn2+ between the beta-TCP and the HA phase in the case of preparation (b) was studied by EPR spectroscopy, and a pronounced preference for the former lattice was found. Micron- and submicron-sized crystals with visible faces were observed by TEM in the case of beta-TCP prepared by solid-state reaction, and large micron-sized, droplike-shaped crystals, sensitive to beam radiation, were found in the case of samples prepared by heating HA at elevated temperatures. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)