Phase Relations and Thermal Expansion Studies in the Ceria–Yttria System

The synthesis, characterization, and bulk and lattice thermal expansions of a series of compounds with general composition Ce 1– x Y x O 2– x /2 (0.0 ≤ x ≤ 1.0) are reported. The XRD pattern of each product was refined to learn the solid solubility limit and the homogeneity range. The solid solubility limit of YO 1.5 in CeO 2 lattice, under the conditions of slow cooling from 1400°C, is represented as Ce 0.55 Y 0.45 O 1.775 (i.e., 45 mol% of YO 1.5 ). The subsequent compositions were biphase. There was no solubility of CeO 2 into the lattice of YO 1.5 . The bulk thermal expansion measurements from ambient to 1123 K, as investigated using a dilatometer, revealed that the α l (293–1123 K) values, within the homogeneity range, decreased on increased Y 3+ content. A similar trend was observed for average lattice thermal expansion coefficient, α a (293–1473 K), as investigated using high‐temperature XRD. No ordered phases were obtained in this system under the used conditions. These studies on Ce 1– x Y x O 2– x /2 (0.0 ≤ x ≤ 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu 1– x Y x O 2– x /2 (0.0 ≤ x ≤ 1.0), because CeO 2 is widely used as a surrogate material for PuO 2 .