Polymorphism and properties of ammonium scandium sulfate (NH₄)₃Sc(SO₄)₃: new intermediate compound in scandium production

Abstract

Discovery of (NH4)3Sc(SO4)3 polymorphs and comprehensive characterization of their structural and thermal properties that can promote extraction and production of scandium.

Co-crystallization of red emitting (NH4)3Sc(SO4)3:Eu3+ microfibers: structure–luminescence relationship for promising application in optical thermometry

“…The details of physical characterization of the phase transition from the LT to HT phase of pristine (NH 4 ) 3 Sc(SO 4 ) 3 were reported previously. 20 Likely, they remain the same for (NH 4 ) 3 Sc(SO 4 ) 3 :0.005Eu 3+ . However, since the optically active Eu 3+ ions have been successfully incorporated into an (NH 4 ) 3 -Sc(SO 4 ) 3 lattice and they may serve as both the probe and the tool, we would like to point out some possible changes occurring in the first coordination sphere of Sc 3+ (Eu 3+ ) ions.…”

“…The details of the synthesis procedure may be found in ref. 20 and in the Experimental section. Co-crystallization of sulfates was carried out according to eqn (1).…”

“…The structural and thermal properties of undoped (NH 4 ) 3 Sc(SO 4 ) 3 were comprehensively studied in ref. 20. According to the results of both high-temperature X-ray diffraction and differential thermal analysis, the compound has two enantiotropic polymorphs at standard pressure: low-temperature monoclinic ( P 2 1 /c , LT, CSD 434420) and high-temperature rhombohedral ( R 3 c , HT, CSD 434422) modifications.…”

“…The (NH 4 ) 3 Sc(SO 4 ) 3 :0.005Eu 3+ compound was obtained via crystallization from an aqueous solution, as described previously for undoped (NH 4 ) 3 Sc(SO 4 ) 3 . 20 The following reagents were used: (NH 4 ) 2 SO 4 (analytical grade, JSC "EKOS-1"), Sc 2 O 3 (99.9%, Lanhit LTD), Eu 2 O 3 (99.999%, %, Lanhit LTD), concentrated sulfuric acid H 2 SO 4 (analytical grade, JSC "EKOS-1"), and rectified 95% ethyl alcohol (5% water, JSC "RFK"). At the first stage, 0.10 mol L −1 Sc 3+ and 0.0065 mol L −1 Eu 3+ sulfate solutions were prepared by dissolving Sc 2 O 3 and Eu 2 O 3 oxides in the presence of H 2 SO 4 (∼1.0-1.5 mol L −1 ) at 353-363 K. At the second stage, 25 mL of the Sc 2 (SO 4 ) 3 (C(Sc 3+ ) = 0.10 mol L −1 ) solution and 25 mL of the Eu 2 (SO 4 ) 3 (C(Eu 3+ ) = 0.0065 mol L −1 ) solution were mixed quickly with 20 mL of the saturated solution of ammonium salt (15 g (NH 4 ) 2 SO 4 ) at 343-353 K. Such a considerable excess of ammonium salt with respect to the scandium content in the solution allows prevention of the formation of NH 4 Sc(SO 4 ) 2 .…”

“…Recently, an enantiotropic first-order phase transition from monoclinic modification (S.G. P 2 1 / c , Z = 4) to rhombohedral structure (S.G. R 3 c , Z = 6) has been revealed in the undoped (NH 4 ) 3 Sc(SO 4 ) 3 sulfate by our group. 20 It was shown that despite the transition not being accompanied by a variation in the coordination number of scandium atoms (CN = 6), the coordination environment of Sc 3+ changes. The reversibility and the relatively low temperature of the polymorphic transition ( T = 354.6 K) prompted an idea to synthesize and to study phosphors with characteristics reflecting the ongoing phase transformations.…”