Phase evolution and microstructure studies on Nd3+ and Ce4+ co-doped zircon ceramics

A series compositions with general stoichiometry as Zr1−x−y(NdxCey)SiO4−x/2 (0 ≤ x, y ≤ 0.1) have been obtained by simultaneous substitution of Nd3+ and Ce4+ for Zr4+ in ZrSiO4 structure. The effects of Nd and Ce content on the phase evolution and microstructure of the ceramics were investigated systematically. The results show that the samples co-doped with total content of Nd3+ (x) and Ce4+ (y) < 0.04 are single zircon phase. However, when the compositions co-doped with total content of Nd3+ (x) and Ce4+ (y) ≥ 0.04 exhibit coexistence of zircon and (Nd,Ce)2Si2O7 phase. This demonstrates that the solubility of Nd3+ and Ce4+ in zircon structure is around 0.04 mol per mol of zircon. In addition, it is found that the densities of the samples increase with increasing total content of Nd3+ and Ce4+. These results indicate that zircon ceramics are promising candidate for the immobilization of trivalent and tetravalent actinides.