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

A series compositions with general stoichiometry as Zr 1− x − y (Nd x Ce y )SiO 4− x /2 (0   ≤   x , y   ≤   0.1) have been obtained by simultaneous substitution of Nd 3+ and Ce 4+ for Zr 4+ in ZrSiO 4 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 Nd 3+ ( x ) and Ce 4+ ( y )   <   0.04 are single zircon phase. However, when the compositions co-doped with total content of Nd 3+ ( x ) and Ce 4+ ( y )   ≥   0.04 exhibit coexistence of zircon and (Nd,Ce) 2 Si 2 O 7 phase. This demonstrates that the solubility of Nd 3+ and Ce 4+ 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 Nd 3+ and Ce 4+ . These results indicate that zircon ceramics are promising candidate for the immobilization of trivalent and tetravalent actinides.