The crystal structures of α and γ SrUO4
Abstract
On rhombohedral strontium monouranate which is metastable below ca. 770°C (α-phase) and stable above ca. 1230°C (γ-phase) in air, x-ray powder diffraction study was made with the samples of three different compositions, i.e. SrUO3.948(1), SrUO3.597(1) and SrUO3.777(1). Their structures were essentially identical with that of Zachariasen (1948) on SrUO4 with space group R[unk]m, Z = 1; 1 U in (000), 1 Sr in (½½½),2 O(1) in ±(uuu) and 2 O(2) in ± (vvv), and no more discrepancies were observed in the cell and the oxygen parameters between α and γ phases than those resulted from the oxygen non-stoichiometry: SrUO3.948(1)a = 6.551(3) Å, α = 34.82(2)°, u = 0.112(2), v = 0.357(2) SrUO3.597(1)a = 6.587(3) Å, α = 35.30(2)°, u = 0.110(2), v = 0.340(2) SrUO3.777<1)a = 6.542(3) Å, α = 35.54(2)°, u = 0.113(2), v = 0.340(2). In oxygen deficient crystals, oxygen vacancies were found to be formed in O(2) position but not in O(1). The U–O(2) bond length 2.30(1) ∼ 2.31(1) Å is reasonably consistent with the other alkali and alkaline-earth uranates, whereas the U–O(1) bond length lies in the range 2.04(4) ∼ 2.08(4) Å which is longer than the usual uranyl bond length of 1.8 ∼ 1.9 Å.
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- Quadratischer elektrostriktiver Tensor des rhombischen Calciumformiats
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