Formation of Open Framework Uranium Germanates: The Influence of Mixed Molten Flux and Charge Density Dependence in U-Silicate and U-Germanate Families

Abstract

Seven novel open-framework uranyl germanates, K(UO)GeO, K(UO)GeO, α-Cs(UO)GeO, β-Cs(UO)GeO, Cs(UO)GeO, and A(UO)(GeO) (A = [NaKCl], [NaCsCl]), were grown from different mixed molten fluxes. The three-dimensional (3D) structure of K(UO)GeO with 8-ring channels can be built upon [UGe] pentamer secondary building units (SBUs). The 3D framework of K(UO)GeO with trapezoid (GeO) clusters consists of two types of [UGe] pentamers. The 3D framework of α-Cs(UO)GeO with 10-ring channels, crystallizing in the P2/ n space group, is constructed by [UGe] pentamers. The structure of β-Cs(UO)GeO contains achter (eight) single germanate chains and is composed of [UGe] heptamers and [UGe] pentamers. The structure of Cs(UO)GeO with hexagonal 10-ring channels is composed of [UGe] heptamers and twisting five-fold GeO tetrahedra in four-membered GeO rings occur. 3D frameworks of NaKCl(UO)(GeO) (space group Pnnm) and NaCsCl(UO)(GeO) ( P2/ c) can be constructed from the same SBUs [UGe] pentamers. Thermal stability of salt-inclusions was studied by TG and PXRD analysis. Analysis of charge density for the U-Si-O system indicates that the polymerization of silicate units reduces the cross-links of the 3D frameworks. The concept of SBUs combined with the cutting and gluing strategy was applied to understand and analyze the distinct 8-, 10-, 12-, and 14- membered channels for the uranyl germanate family. The charge density of all known 3D U-Si/Ge-O frameworks has been investigated, which shows strong correlations with chemical composition of corresponding phases. The increase of Si/O (Ge/O) ratios in silicate units results in the decrease of negative charge density. Moreover, the charge density increases with decreasing countercation size within the same Si/O ratio. The correlations can be used to predict inclusion phase formation within U-Si/Ge-O families. Raman spectra of the studied uranyl germanates were measured, and bands were assigned on the basis of structural features.

Inorganic X-ray Scintillators Based on a Previously Unnoticed but Intrinsically Advantageous Metal Center

“…The refinement result is shown in Table . We further determined the unit cell parameters of UBO , UPO , and UGO , which are in agreement with the reported values. − Only the refinement results of UMO are shown in this work.…”

“…We collected the UV- and X-ray excited luminescence spectra of the selected uranyl-bearing inorganic compounds, as shown in Figure S2 (Supporting Information). The UV excited spectra of Na­(UO 2 )­B 6 O 10 (OH)·2H 2 O ( UBO ), K­(UO 2 )­(PO 4 )·4H 2 O ( UPO ), Na 2 (UO 2 )­GeO 4 ( UGO ), and Na 2 (UO 2 )­(MoO 4 ) 2 ·(H 2 O) ( UMO ) exhibit the intrinsic green emission with similar peak shapes and positions. In addition, the X-ray excited spectra of UBO and UMO fully duplicate the corresponding UV excited spectra, confirming the nature of self-activated scintillator (Figure S2).…”

Flux Growth of Uranyl Titanates: Rare Examples of TiO4 Tetrahedra and TiO5 Square Bipyramids

“…For much of their history, the focus was on the investigation of uranyl minerals and the exploration of new materials through ceramic and hydrothermal syntheses, the latter of which resembles the conditions under which most minerals form. In the past decade, the flux growth of uranyl compounds, especially using halide fluxes, has become quite prolific, resulting in many new uranyl silicates, − germanates, − phosphates, − borates, − aluminates, and others. ,, …”

3d-Metal Induced Magnetic Ordering on U(IV) Atoms as a Route toward U(IV) Magnetic Materials

“…Uranium exhibits a wide range of oxidation states, ranging from +2 to +6, − with the +4 and +6 states being most prevalent in the solid state. The +6 state is exceptionally stable at elevated temperatures in air, making U­(VI) compounds among the most studied phases of existing uranium compounds. − Fully oxidized uranium, however, has an empty 5 f shell and is thus of little interest for the purpose of studying the magnetic behavior of 5 f electrons. On the other hand, reduced uranium compounds having 5 f electron(s) present a valuable opportunity to study their magnetic behavior; complex cases involving exchange coupling with other magnetic elements are of particular interest. − An understanding of U­(IV) compounds magnetic properties has not been fully developed as a result of several challenges posed.…”