From thorium phosphate hydrogenphosphate hydrate to β\beta-thorium phosphate diphosphate: Structural evolution to a radwaste storage ceramic

$\beta$-Thorium phosphate diphosphate ($\beta$-TPD), considered as a very promising radwaste storage material, was obtained from thorium phosphate hydrogenphosphate hydrate (TPHPH) precursor through dehydration and hydrogen phosphate condensation. The structures of TPHPH, intermediate $\alpha$-thorium phosphate diphosphate ($\alpha$-TPD) and its hydrate ($\alpha$-TPDH) have been resolved ab initio by Rietveld analysis of their synchrotron diffraction patterns. All were found orthorhombic (space group Cmcm) and similarly composed of [ThPO$_4$]$_4^{4+}$ slabs alternating with disordered layers hosting either [HPO$_4$·H$_2$O]$_2^{4-}$ (TPHPH), [P$_2$O$_7$·2H$_2$O]$^{4-} ($\alpha$-TPDH), or [P$_2O_7$]$^{4-}$($\alpha$-TPD), unlike the 3D structure of$\beta$-TPD. The diphosphate groups of$\alpha$-TPD and$\alpha$-TPDH are strongly bent. The irreversible transition to the final$\beta$-TPD consists in a shearing of the slabs and a reduction of the interslabs cavities that explains the stability of this high-temperature form

Crystal data for <i>Cu</i>₂<i>Th</i>₄(<i>MoO</i>₄)₉ and isostructural compounds

Cu2Th4(MoO4)9 is cubic: a=14.4856(1) Å, space group I4¯3d, Z=4. Its crystal structure was recently determined using a single crystal. The results of chemical study allow one to reject the existence of Li4Th7(MO4)16 and La(MO4)(ReO4) compounds with M=Mo, W, reported as isostructural with Cu2Th4(MoO4)9. Precise X-ray powder patterns are established for Cu2Th4(MoO4)9 and isotypic compounds Li2Th4(MoO4)9, Li2Th4(WO4)9, and La4(MoO4)3(ReO4)6.</jats:p

Données cristallines de deux molybdates MIV(MoO4)2 avec MIV= Zr, Hf

peer reviewedTwo molybdates MIV(MoO4)2 (with MIV = Hf or Zr) were synthesized by solid state reaction between MIVO2 and MoO3. Zirconium molybdate undergoes a reversible phase transition at 952 K. Hf(MoO4)2 and H.T. Zr(MoO4)2, obtained as single crystals, are trigonal, space group P31c with Z = 6; the cell dimensions are respectively a = 10.1005(3), c = 11.7230(5)Å V = 1035.76(11)Å3; Dm(298 K) = 4.78(4), Dx = 4.792 Mg m-3 and a = 10.1409(3), c = 11.7097(5)Å V = 1042.88(11)Å3; Dm (298 K) = 3.91(4), Dx = 3.926 Mg m-3. L.T. Zr(MoO4)2, indexed by the Visser automatic indexing program (1969) was found to be monoclinic, possible space group P2, P21 or Pm with Z = 4; the cell dimensions are a - 9.7557(5), b = 7.9373(5), c = 7.4631(4)Å, β = 97.959°(5); V = 572.3(5)Å Dm(298 K) - 4.74(5), Dx = 4.770 Mg m−3. Powder diffraction data were obtained at 293 K on a counter diffractometer with Ni-filtered copper radiation (̄λ = 1.5418 Å). © 1987, Cambridge University Press. All rights reserved

Revised Crystal Data of Zr(MoO₄)₂, L.T. Form

AbstractZr(MoO4)2 molybdate has been synthesized by solid state reaction. Single crystals were obtained by hydrothermal synthesis. Corrected crystal data are: monoclinic, a = 11.4309 (3), b = 7.9376 (2), c = 7.4619 (2) Å and β = 122.323 (2)°, V = 572.13 (6) /cm3 (5), Dx = 4.770 g/cm3. Powder diffraction data are reported.</jats:p

Synthesis and crystal data for K₃Nb₃O₆Si₂O₇

The silicate compound, K3Nb3O6Si2O7, has been synthesized by solid-state reaction. Single crystals were obtained; they crystallized with the hexagonal space group P2c. Refined unit-cell parameters are: a = 9.0377(3), c=8.0465(7)Å, V=569.18(5)Å3, Z=2, Dm = 3.84(4), Dx=3.851. Powder diffraction data are reported.</jats:p