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

Abstract

The synthesis, characterization, and bulk and lattice thermal expansions of a series of compounds with general composition Ce1–xYxO2–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 YO1.5 in CeO2 lattice, under the conditions of slow cooling from 1400°C, is represented as Ce0.55Y0.45O1.775 (i.e., 45 mol% of YO1.5). The subsequent compositions were biphase. There was no solubility of CeO2 into the lattice of YO1.5. The bulk thermal expansion measurements from ambient to 1123 K, as investigated using a dilatometer, revealed that the αl (293–1123 K) values, within the homogeneity range, decreased on increased Y3+ content. A similar trend was observed for average lattice thermal expansion coefficient, αa (293–1473 K), as investigated using high‐temperature XRD. No ordered phases were obtained in this system under the used conditions. These studies on Ce1–xYxO2–x/2 (0.0 ≤x≤ 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu1–xYxO2–x/2 (0.0 ≤x≤ 1.0), because CeO2 is widely used as a surrogate material for PuO2.