Lattice parameter and thermal conductivity of Th1−xMxO2−y (M = Y, La, Ce, Nd, Gd and U)

High-density Th1−xMxO2−y (M = Y, La, Ce, Nd, Gd and U; x = 0.05 and 0.10) samples were fabricated by solid-state reaction followed by Spark plasma sintering. The lattice parameter changed linearly with the ionic radius of the M atom and the amount of oxygen defect. A simple formula is proposed for the lattice parameter expectation. The thermal conductivity decreased according to the differences in atomic mass and ionic radius. For trivalent ion-added samples, the oxygen defect significantly decreased the thermal conductivity. These effects were analyzed using the Klemens–Callaway model, which enables an estimation of the lattice thermal conductivity for the fission product–containing ThO2 matrix.