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Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties
Published on: August 15, 2015
Structure and Thermal Expansion of Calcium-Thorium Apatite, [Ca4]F[Ca2Th4]T[(SiO4)6]O2
Evgeny N Bulanov1, Jingxian Wang2, Alexander V Knyazev1
1Lobachevsky State University of Nizhni Novgorod , Nizhni Novgorod, Russia.
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.
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