Abstract
Langbeinite is proposed as a promising host matrix for radioactive wastes, but no structures incorporating actinides have been reported yet. In this work, a series of single crystals of Cs(2)U(Ⅳ)Ln(PO(4))(3) (Ln = Ce - Nd and Sm - Lu), the first reported langbeinite-type structure incorporating actinides (U(IV)) which crystallizes in the cubic space group P2(1)3, have been successfully prepared by optimizing the high-temperature molten salt method. Their 3D frameworks are characterized by a typical langbeinite structure with U/Ln co-occupying six-coordinated octahedra and Cs cations filling closed large-sized cavities. The compounds exhibit high thermal stability up to 1200 °C under N(2) and show outstanding leaching resistance, with the leaching rates of U and Nd at 10(-8) g·m(-2)·d(-1) and Cs 10(-3) g·m(-2)·d(-1). This study highlights the potential of langbeinite-type structures for effectively immobilizing both tetravalent and trivalent actinides as promising waste forms.