On the Formation of Americium-and Neptunium-Containing Titanates

Abstract

The Compound AmzTijOy with americium in the III oxidation State was synthesized and characterized as exhibiting monoclinic symmetry. Solid solutions between monoclinic AmzTizO, and a representative cubic pyrochlore, EfjTijO,, were prepared, and the solubihty limit of AmjTijO, was determined to be 59 ±9 mol percent. The preparation of strontium-containing perovskite Compounds of the type Sr4_^m2^/3Ti40i2 and Sr6-,2,Ani6jTi50,6 were attempted. Only the tetragonally-distorted SrAm2Ti40,2, with americium in the III oxidation State, was formed while SraAmjTijOis, with americium in the IV oxidation State, could not be prepared. Attempted syntheses of analogous Np(III) and Np(IV) Compounds were unsuccessful.

Phase Evolution in the CaZrTi2O7–Dy2Ti2O7 System: A Potential Host Phase for Minor Actinide Immobilization

“…Further confidence in Dy oxidation state assignment was informed from bond valence sum analyses, the results of which are summarized in Table . The speciation of Dy 3+ is encouraging, as this remains comparable to Am 3+ ; previously, the synthesis of Am 2 Ti 2 O 7 by calcination in air between 1200 and 1300 °C has been shown to result in the complete reduction of Am 4+ to Am 3+ . Feature B presented a variation that may be dependent on the coordination of Dy 3+ cations.…”

“…The speciation of Dy 3+ is encouraging, as this remains comparable to Am 3+ ; previously, the synthesis of Am 2 Ti 2 O 7 by calcination in air between 1200 and 1300 °C has been shown to result in the complete reduction of Am 4+ to Am 3+ . 45 Feature B presented a variation that may be dependent on the coordination of Dy 3+ cations. This is evidenced by the reference compounds (Dy 2 TiO 5 and Dy 2 O 3 ) having different energy maxima (∼7812.4 eV) compared to the Dy-titanates x = 0.10, 0.30, 0.60, and 1.00 (Dy 2 Ti 2 O 7 ) (∼7815.9 eV) ( Figure 9 and Table S2 ).…”

Zirconolite Polytypes and Murataite Polysomes in Matrices for the REE—Actinide Fraction of HLW

“…For fractions of trivalent minor actinides (MA–Am, Cm) and REE–MA, Nd 3+ serves as an optimal simulator due to the proximity of ionic radii in the corresponding coordination [ 48 , 107 ]. Their compounds have the same structure, for example monoclinic perovskite-like for Nd 2 Ti 2 O 7 and Am 2 Ti 2 O 7 [ 149 ], whilst REE titanates with a radius smaller than that of Nd 3+ form a cubic pyrochlore structure. Hence, the use of Dy 3+ as an simulator of Am 3+ and other trivalent actinides is not quite correct [ 150 ].…”