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

Abstract

A series of Nd and Ce co-doped (Gd1−xNdx)2(Zr1−xCex)2O7 (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 (Gd1−xNdx)2(Zr1−xCex)2O7 (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 Gd2Zr2O7 pyrochlore structure, respectively. The normalized release rates of Gd, Zr, Nd and Ce in (Gd1−xNdx)2(Zr1−xCex)2O7 pyrochlore bulk ceramics (x = 0.25, 0.5 and 0.75) remained relatively constant in a low value below 10−4gm−2d−1 at 90°C for 7 days, exhibiting superior chemical stability.