Rare earth substituted fluoride-phosphate apatites

Abstract

Compositions with the general formula Ln xM 10−2xNa x(PO 4) 6F 2 (Ln = La, Pi, Nd, Sm, Eu, Dy, Er, Lu, andY;M = Ca, Sr, and Ba) have been prepared and studied by X-ray diffraction methods. The hexagonal apatite like structure was indicated by the powder patterns of all the compounds (with Ba compounds only when Ln = La through Sm). Single crystal precession data reveal that the crystal lattice of all the compositions in the Ca and Sr system have space group P6 3/ m, the Ln 2Ba 6Na 2(PO 4) 6F 2 compounds crystallize in space group P6 and the Ln 3Ba 4Na 3(PO 4) 6F 2 compounds in the trigonal space group P3. Order and disorder mechanisms of the substitution and its dependence on size and polarization effects are discussed.