X-ray and thermal investigations of [(U0.2Th0.8)1−yDyy]O2+x; 0 ≤ y ≤ 0.37

Abstract Phase relations and defect structures in (U 0.2 Th 0.8 )O 2 -DyO 1.5 quaternary system were studied at 1673 K by heating the oxides in different atmospheres. Lattice parameter and O/U of the mixed oxides were determined from X-ray diffraction (XRD) and chemical analysis, respectively. The cubic lattice parameter of [(U 0.2 Th 0.8 ) 1−y Dy y ]O 2+x ; (0 ≤ y ≤ 0.37) could be expressed in a linear equation of x and y as: a 0 ( A ′ ) = 5.5709 − 0.132 x − 0.164 y; for x 0 and 0 ≤ y ≤ 0.37 Thermogravimetric study of [(U 0.2 Th 0.8 ) 1−y Dy y ]O 2+x ; y = 0 to 0.27 in air showed single step oxidation and retain the fluorite structure. High temperature X-ray diffraction (HTXRD) study of [(U 0.2 Th 0.8 ) 1−y Dy y ]O 2+x showed positive thermal expansion between 298 and 1273 K. The specific heat capacities of these solid solutions, measured using differential scanning calorimetry from 300 to 850 K, showed decreasing trend with increasing Dy content.