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

Abstract

Neodymium is typically considered the best surrogate for trivalent americium and can be used to identify Am 3+ 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 AE 5 Ln-(BO 3 ) 4 X (AE = Ca, Sr; Ln = Pr, Nd, Eu, Tb; X = Cl, Br) and AE 3 Ln 2 (BO 3 ) 4 (AE = Sr, Ba; Ln = Pr, Nd) as well as the synthesis of two compounds of Ba 8 Ln 2 (BO 3 ) 6 (B 2 O 5 ) (Ln = Eu, Tb) crystallizing in a new structure type. Ba 8 Ln 2 (BO 3 ) 6 (B 2 O 5 ) crystallizes in the space group P2 1 /n with lattice parameters a = 8.6002(3) Å, b = 7.9245(3) Å, c = 17.6697(7) Å, and β = 91.3560(10)°for the Eu analogue, and the structure contains isolated LnO 8 polyhedra connected into a framework by BO 3 and B 2 O 5 units. The fluorescence emission spectra of AE 5 Ln(BO 3 ) 4 X (AE = Ca, Sr; Ln = Eu, Tb; X = Cl, Br) and Ba 8 Ln 2 (BO 3 ) 6 (B 2 O 5 ) (Ln = Eu, Tb) are reported.