title: Structure and Thermal Expansion of Calcium-Thorium Apatite, [Ca4]F[Ca2Th4]T[(SiO4)6]O2.
abstract: Thorium silicate apatite with the formula [Ca3.84Th0.16]F[Ca2.79Th3.21]T(SiO4)6O2 · x(H) was synthesized by solid-state reaction, and its structure refined in P63/m from powder X-ray diffraction (XRD) data using the Rietveld method (a = 9.50172(9) Å, c = 6.98302(8) Å, V = 545.98(1) Å(3); R-Bragg = 2.102%). It was found that thorium partitions strongly to the tunnel (T) 6h position rather than the framework (F) 4f site. Fourier transform infrared spectroscopy revealed only SiO4 tetrahedron, with SiO5 and SiO6 groups, sometimes observed in siliceous apatites absent, at least to the limit of detection of this technique. Thermal expansion of the thorium apatite determined by high-temperature XRD from 298-1173 K found Δa (0.87%) dilation to exceed Δc (0.73%) with increasing temperature consistent with other silicate apatites.
authors.affiliation: Lobachevsky State University of Nizhni Novgorod , Nizhni Novgorod, Russia.
authors.forename: Evgeny N
authors.initials: EN
authors.lastname: Bulanov
authors.affiliation: Nanyang Technological University , Singapore.
authors.forename: Jingxian
authors.initials: J
authors.lastname: Wang
authors.affiliation: Lobachevsky State University of Nizhni Novgorod , Nizhni Novgorod, Russia.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Knyazev
authors.affiliation: Nanyang Technological University , Singapore.
authors.forename: Tim
authors.initials: T
authors.lastname: White
authors.affiliation: Lobachevsky State University of Nizhni Novgorod , Nizhni Novgorod, Russia.
authors.forename: Marina E
authors.initials: ME
authors.lastname: Manyakina
authors.affiliation: Nanyang Technological University , Singapore.
authors.forename: Tom
authors.initials: T
authors.lastname: Baikie
authors.affiliation: Bruker Ltd , Moscow, Russia.
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Lapshin
authors.affiliation: Nanyang Technological University , Singapore.
authors.forename: ZhiLi
authors.initials: Z
authors.lastname: Dong