Flux synthesis and chemical stability of Nd and Ce co-doped (Gd1−xNdx)2(Zr1−xCex)2O7 (0 ≤ x ≤ 1) pyrochlore ceramics for nuclear waste forms

A series of Nd and Ce co-doped (Gd 1−x Nd x ) 2 (Zr 1−x Ce x ) 2 O 7 (0 ≤ x ≤ 1) pyrochlores were synthesized by flux method at 900–1000   °C using nitrates as starting materials and a small amount of NaF as fluxing agent . The influences of contents of Nd/Ce, fluxing agent and reaction temperature on the phase structure of the pyrochlores were systematically investigated by X-ray diffraction (XRD) and Raman spectroscopy (Raman). The chemical stability of Nd and Ce co-doped pyrochlore bulk ceramics was also evaluated. XRD and Raman results showed that the crystalline phase of (Gd 1−x Nd x ) 2 (Zr 1−x Ce x ) 2 O 7 (0 ≤ x ≤ 1) pyrochlores always remained a single disordered defect-fluorite structure for any x value. XRD, Raman spectrum and SEM-EDX results revealed that the Nd and Ce could be co-doped at the Gd-site and Zr-site of the Gd 2 Zr 2 O 7 pyrochlore structure, respectively. The normalized release rates of Gd, Zr, Nd and Ce in (Gd 1−x Nd x ) 2 (Zr 1−x Ce x ) 2 O 7 pyrochlore bulk ceramics (x = 0.25, 0.5 and 0.75) remained relatively constant in a low value below 10 −4   g   m −2   d −1 at 90   °C for 7 days, exhibiting superior chemical stability.