Incorporation of Rare Earth Elements into (Ba,ca)2(co3…
Solid state sciences(2023)
Abstract
The structural effects of the incorporation of the rare earth elements (REE) La, Ce, Pr, Nd, Eu, Sm, Gd, Er, Tm, Yb and Y into a synthetic Ba–Ca carbonate have been investigated. We precipitated solutions with a composition Ba0.9Ca1.1(CO3)2 doped with REE-nitrates. The precipitate, with few exceptions, consisted of a crystalline solid, slightly depleted in Ba with respect to the expected composition, and an amorphous phase. On heating, the whole sample became crystalline and consisted of a Ba-enriched and a Ba-depleted phase. The phases are isostructural. The lattice parameters are strongly influenced by the incorporation of ≈ 6% REE. There is a linear dependence of the unit cell volume on the radius of the incorporated REE for those elements with a radius < 1.0 Å, i.e. Yb, Tm, Er, Y, Gd, Sm, Eu, Nd and Pr, while the unit cell volume of a sample doped with La (r(La) = 1.03 Å) and Ce (r(Ce) = 1.01 Å) is not well described by this dependency. Raman spectroscopy shows that the local environment of the CO3-groups does not differ substantially between the Ba-enriched and the Ba-depleted phase, but changes linearly as a function of the ionic radius of the REE. The present study clearly shows that substantial amounts of REE can be incorporated into the Ba–Ca-carbonate studied here, making it potentially useful as a matrix in nuclear waste treatments involving aqueous nitrate solutions of lanthanides and actinides.
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