title: Crystal structure of apatite type Ca2.49Nd7.51(SiO4)6O1.75.
abstract: The title compound, Ca2+x Nd8-x (SiO4)6O2-0.5x (x = 0.49), was synthesized at 1873 K and rapidly quenched to room temperature. Its structure has been determined using single-crystal X-ray diffraction and compared with results reported using neutron and X-ray powder diffraction from samples prepared by slow cooling. The single-crystal structure from room temperature data was found to belong to the space group P63/m and has the composition Ca2.49Nd7.51(SiO4)6O1.75 [dicalcium octa-neodymium hexa-kis-(ortho-silicate) dioxide], being isotypic with natural apatite and the previously reported Ca2Nd8(SiO4)6O2 and Ca2.2Nd7.8(SiO4)6O1.9. The solubility limit of calcium in the equilibrium state at 1873 K was found to occur at a composition of Ca2+x Nd8-x (SiO4)6O2-0.5x , where x = 0.49.
authors.affiliation: KU Leuven - University of Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44 - bus 2450, B-3001 Heverlee, Belgium.
authors.forename: Thu Hoai
authors.initials: TH
authors.lastname: Le
authors.affiliation: KU Leuven - University of Leuven, Department of Chemistry, Celestijnenlaan 200F - bus 2404, B-3001 Heverlee, Belgium.
authors.forename: Neil R
authors.initials: NR
authors.lastname: Brooks
authors.affiliation: KU Leuven - University of Leuven, Department of Chemistry, Celestijnenlaan 200F - bus 2404, B-3001 Heverlee, Belgium.
authors.forename: Koen
authors.initials: K
authors.lastname: Binnemans
authors.affiliation: KU Leuven - University of Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44 - bus 2450, B-3001 Heverlee, Belgium.
authors.forename: Bart
authors.initials: B
authors.lastname: Blanpain
authors.affiliation: KU Leuven - University of Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44 - bus 2450, B-3001 Heverlee, Belgium.
authors.forename: Muxing
authors.initials: M
authors.lastname: Guo
authors.affiliation: KU Leuven - University of Leuven, Department of Chemistry, Celestijnenlaan 200F - bus 2404, B-3001 Heverlee, Belgium.
authors.forename: Luc
authors.initials: L
authors.lastname: Van Meervelt
keywords: apatite structure type; calcium rare earth oxide silicate; crystal structure