Crystallization of A3Ln(BO3)2 (A = Na, K; Ln = Lanthanide) from a Boric Acid Containing Hydroxide Melt: Synthesis and Investigation of Lanthanide Borates as Potential Nuclear Waste Forms

A series of alkali metal rare-earth borates were prepared via high temperature flux crystal growth, and their structures were characterized by single crystal X-ray diffraction (SXRD). Na(3)Ln(BO3)(2) (Ln = La-Lu) crystallize in the monoclinic space group P21/n, the potassium series K(3)Ln(BO3)(2) (Ln = La-Tb) crystallize in the orthorhombic space group Pnma, while the Ln = Dy, Ho, Tm, Yb analogues crystallize in the orthorhombic space group Pnnm. To demonstrate the generality of this synthetic technique, high-entropy oxide (HEO) compositions K3N d (0 . 1 5( 1 ))E u(0. 2 0 ( 1 ) )G d( 0 . 2 0 ( 1 ))D (y0. 2 2 ( 1 )) H o (0 . 2 3 ( 1 ))( B O- 3 ) (2) and K3Nd0.26(1)Eu0.29(1)Ho0.22(1)Tm0.14(1)Yb0.10(1)(BO3)(2) were obtained in single crystal form. Radiation damage investigations determined that these borates have a high radiation damage tolerance. To assess whether trivalent actinide analogues of Na(3)Ln(BO3)(2) and K(3)Ln(BO3)(2) would be stable, density functional theory was used to calculate their enthalpies of formation, which are favorable.

Automated summary

A series of alkali metal rare-earth borates were synthesized and characterized. The borates exhibit high radiation damage tolerance and the trivalent actinide analogues are predicted to be stable.