Phase relations and linear thermal expansion of cubic solid solutions in the Th1−xMxO2−x/2 (M = Eu, Gd, Dy) systems

Cell parameters and linear thermal expansion studies of the Th–M oxide systems with general compositions Th1−xMxO2−x/2 (M = Eu3+, Gd3+ and Dy3+, 0.0 ⩽ x ⩽ 1.0) are reported. The XRD patterns of each product were refined to specify the solid solubility limits of MO1.5 in the ThO2 lattice. The upper solid solubility limits of EuO1.5, GdO1.5 and DyO1.5 in the ThO2 lattice under conditions of slow cooling from 1673 K are represented as Th0.50Eu0.50O1.75, Th0.60Gd0.40O1.80 and Th0.85Dy0.15O1.925, respectively. The linear thermal expansion (293–1123 K) of MO1.5 and their single-phase solid solutions with thoria were investigated by dilatometery. The average linear thermal expansion coefficients ( α ¯ ) of the compounds decrease on going from EuO1.5 to DyO1.5. The values of α ¯ for EuO1.5, GdO1.5 and DyO1.5 containing solid solutions showed a downward trend as a function of the dopant concentration. The linear thermal expansion (293–1473 K) of the solid solutions investigated by high-temperature XRD also showed a similar trend.