Three uranyl silicate framework structures, Cs1.8K0.2[(UO2)(Si2O6)], K4Sr[(UO2)(Si4O12)], and [Cs2KF][(UO2)(Si4O10)], and theoretical calculation of density functional theory for salt-inclusion material

Single crystals of three new uranyl silicates were grown from mixed alkali fluoride fluxes. Cs_1.8K_0.2[(UO₂)(Si₂O₆)] crystallizes in the space group C2/c and lattice parameters a = 21.5486(11) Å, b = 15.1071(8) Å, c = 14.8947(14) Å, and β = 129.267(2), which is isostructural to the known α-Cs₂[(UO₂)(Si₂O₆)] phase. The new framework K₄Sr[(UO₂)(Si₄O₁₂)] is compared with the related K₄SrU₃O₁₂, and crystallizes in the tetragonal space group P—4n2 with lattice parameters a = 9.3808(3) Å, b = 9.3808(3) Å, c = 8.5234(4) Å. A new salt-inclusion material (SIMs) [Cs₂KF][(UO₂)(Si₄O₁₀)] is compared and discussed with previously reported SIM [Cs₃F][(UO₂)(Si₄O₁₀)], which crystallizes in the space group I2/c and lattice parameters a = 7.5400(3) Å, b = 12.6143(7) Å, c = 14.9686(8) Å, and β = 93.032(3)°. The Raman spectra of these phases were collected, and bands were assigned according to the existing oxo-silicate and oxo-uranium units. The formation enthalpy, lattice energy and band gap of the salt-inclusion materials were calculated by density functional theory to provide more structural information.