Charge compensation mechanisms in U1-xGdxO2 and Th1-xGdxO2-x/2 studied by X-ray Absorption Spectroscopy

The charge compensation mechanisms in U1-xGdxO2 and Th1-xGdxO2-x/2 have been systematically studied using X-ray Absorption Spectroscopy (XAS) upon gradually increasing the Gd content. Our XAS results for a series of technologically relevant Gd contents in U1-xGdxO2 clearly demonstrate that upon increasing the Gd content U5+ is formed inducing slight increase in the U coordination number and contraction for the U-O distances while the Gd local environment remains virtually unchanged. For the Th1-xGdxO2-x/2 larger Gd fractions were applied (x ¼ 0.10 to 0.34). Nonetheless, both Gd and Th local environments show changes upon increasing the Gd content; the average Gd-O and Th-O distances decrease gradually and the Gd and Th coordination numbers follow the expected trend considering the O vacancy formation to obtain charge neutrality.