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 Ce_1–xY_xO_1–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 CeO₂ lattice, under the conditions of slow cooling from 1400°C, is represented as Ce_0.55Y_0.45O_1.775 (i.e., 45 mol% of YO_1.5). The subsequent compositions were biphase. There was no solubility of CeO₂ 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 α₁ (293–1123 K) values, within the homogeneity range, decreased on increased Y³⁺ 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–xY_xO_1–x/2 (0.0 ≤x≤ 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu_1–xY_xO_1–x/2 (0.0 ≤x≤ 1.0), because CeO₂ is widely used as a surrogate material for PuO₂.