Phase relations and linear thermal expansion of cubic solid solutions in the Th 1− xM xO 2− x/2 (M = Eu, Gd, Dy) systems

Abstract

Cell parameters and linear thermal expansion studies of the Th–M oxide systems with general compositions Th 1− x M x O 2− x/2 (M = Eu 3+, Gd 3+ and Dy 3+, 0.0 ⩽ x ⩽ 1.0) are reported. The XRD patterns of each product were refined to specify the solid solubility limits of MO 1.5 in the ThO 2 lattice. The upper solid solubility limits of EuO 1.5, GdO 1.5 and DyO 1.5 in the ThO 2 lattice under conditions of slow cooling from 1673 K are represented as Th 0.50Eu 0.50O 1.75, Th 0.60Gd 0.40O 1.80 and Th 0.85Dy 0.15O 1.925, respectively. The linear thermal expansion (293–1123 K) of MO 1.5 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 EuO 1.5 to DyO 1.5. The values of α ¯ for EuO 1.5, GdO 1.5 and DyO 1.5 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.