Synthesis and characterisation of Pu-doped zirconolites –(Ca_1−xPu_x)Zr(Ti_2-2xFe_2x)O₇

Synchrotron x‐ray spectroscopy investigation of the Ca1−xLnxZrTi2−x(Al, Fe)xO7 zirconolite ceramics (Ln = La, Nd, Gd, Ho, Yb)

“…In comparison with the standard powder diffraction data, the weak peak at 13.36° can be attributed to zirconia. In addition, the SXRD reflections of Ca 0.1 Yb 0.9 ZrTi 1.1 (Al, Fe) 0.9 O 7 sample are similar to zirconolite‐3T from Gilbert et al research . Furthermore, the diffraction lines are also similar to XRD patterns of Ca 1− x Yb x ZrTi 2− x Fe x O 7 for x = 0.8‐0.9 .…”

“…For the Ca 1− x Nd x ZrTi 2− x Al x O 7 solid solution, it was confirmed that the phase transformation from zirconolite‐2M to zirconolite‐3O was at x = 0.6‐0.7 . Gilbert et al found that the solubility of Pu can be up to 0.4 and the zirconolite‐2M transforms to zirconolite‐3T at x = 0.3 in the (Ca 1− x Pu x )Zr(Ti 2−2 x Fe 2 x )O 7 solid solutions . For the Ca 1− x Gd x ZrTi 2− x Al x O 7 samples prepared at 1400°C, Stefanovsky et al pointed out that the zirconolite‐2M is stable up to x = 0.2 and it is likely to form higher symmetry structure (zirconolite‐3T or 6T) in the range of 0.2 < x ≤ 1 .…”

“…For instance, zirconolite‐3O (three‐layer orthorhombic polytype), zirconolite‐3T (three‐layer trigonal polytype), zirconolite‐4M (four‐layer monoclinic polytype), and zirconolite‐6T (six‐layer trigonal polytype) . In the literature, zirconolite has been intensively studied on the solubility and phase transformation when incorporating different actinides/lanthanides cations . Many researchers focused on doping rare earth elements (REE) (as the simulation of radioactive actinides) on both Ca and Zr site of zirconolite, that is, Ca 1− x REE 2 x Zr 1− x Ti 2 O 7 (REE = Ce, Nd, Gd, Sm, Y) .…”

“…21 In the literature, zirconolite has been intensively studied on the solubility and phase transformation when incorporating different actinides/lanthanides cations. 1,[14][15][16][22][23][24][25][26] Many researchers focused on doping rare earth elements (REE) (as the simulation of radioactive actinides) on both Ca and Zr site of zirconolite, that is, Ca 1−x REE 2x Zr 1−x Ti 2 O 7 (REE = Ce, Nd, Gd, Sm, Y). 1,14,[25][26][27][28] Their results showed phase evolution from zirconolite-2M to zirconolite-4M and zirconolite-4M to pyrochlore when doping different amounts of REE.…”

Structural Transformations and Disordering in Zirconolite (CaZrTi2O7) at High Pressure

“…8,9 Synthetic analogues of natural zirconolite, based on the formula CaZrTi 2 O 7 , target substitution of trivalent and tetravalent actinides and lanthanide fission products on the Ca and Zr sites based on the comparable ionic radii of these species, with charge compensation introduced on the Ti site as necessary. [10][11][12][13][14][15] Actinide species incorporated within host crystalline lattices undergo alpha decay processes resulting in substantial structural damage that may eventually result in a radiation amorphized or "metamict" material as reviewed by Weber et al 16 For example, α-decay of Pu-239 affords an energetic (5.2 MeV) α-particle and a U--particle deposits its energy in ionisation processes causing relatively few atomic displacements, but recoil of the daughter atom produces 10 3 atomic displacements through ballistic collisions, within a 10 2 nm cascade. 16 Defect accumulation and cascade overlap eventually result in amorphization of the initially crystalline host material.…”