Two tetravalent uranium silicate and germanate crystals with three membered single-ring by molten salt method: K2USi3O9 and Cs2UGe3O9

Abstract

Two tetravalent uranium silicate and germanate M2UIVT3O9 (M = K, Cs; T = Si, Ge) crystals were crystalized under inert gas by molten salt flux growth method. K2USi3O9 (1) crystallizes in the monoclinic space group P121/n1 with lattice parameters a = 7.1076 Å, b = 10.4776 Å, c = 12.2957 Å, γ = 120° and V = 915.67 Å3. Cs2UGe3O9 (2) crystallizes in a hexagonal space group P-6 with lattice constants of a = 7.5138 Å, b = 7.5138 Å, c = 11.0114 Å, γ = 120° and V = 538.38 Å3. Bond valence calculations indicate tetravalent uranium in both structures, which contain three-membered single-ring T3O96− trimers. K2USi3O9 is the first uranium silicate that contains the Si3O96− trimers.