Flux Synthesis of Alkaline-Earth Lanthanide Borates as Potential Nuclear Waste Forms.

Neodymium is typically considered the best surrogate for trivalent americium and can be used to identify Am containing materials that are likely to form. We have explored the alkaline-earth lanthanide borate phase space using alkaline-earth halide/carbonate fluxes. This resulted in the synthesis of new compounds AELn(BO)X (AE = Ca, Sr; Ln = Pr, Nd, Eu, Tb; X = Cl, Br) and AELn(BO) (AE = Sr, Ba; Ln = Pr, Nd) as well as the synthesis of two compounds of BaLn(BO)(BO) (Ln = Eu, Tb) crystallizing in a new structure type. BaLn(BO)(BO) crystallizes in the space group 2/ with lattice parameters = 8.6002(3) Å, = 7.9245(3) Å, = 17.6697(7) Å, and β = 91.3560(10)° for the Eu analogue, and the structure contains isolated LnO polyhedra connected into a framework by BO and BO units. The fluorescence emission spectra of AELn(BO)X (AE = Ca, Sr; Ln = Eu, Tb; X = Cl, Br) and BaLn(BO)(BO) (Ln = Eu, Tb) are reported.