Anelastic and Electromechanical Properties of Doped and Reduced Ceria

Abstract

Room-temperature mechanical properties of thin films and ceramics of doped and undoped ceria are reviewed with an emphasis on the anelastic behavior of the material. Notably, the unrelaxed Young's modulus of Gd-doped ceria ceramics measured by ultrasonic pulse-echo techniques is >200 GPa, while the relaxed biaxial modulus, calculated from the stress/strain ratio of thin films, is ≈10 times smaller. Oxygen-deficient ceria exhibits a number of anelastic effects, such as hysteresis of the lattice parameter, strain-dependent Poisson's ratio, room-temperature creep, and nonclassical electrostriction. Methods of measuring these properties are discussed, as well as the applicability of Raman spectroscopy for evaluating strain in thin films of Gd-doped ceria. Special attention is paid to detection of the time dependence of anelastic effects. Both the practical advantages and disadvantages of anelasticity on the design and stability of microscopic devices dependent on ceria thin films are discussed, and methods of mitigating the latter are suggested, with the aim of providing a cautionary note for materials scientists and engineers designing devices containing thin films or bulk ceria, as well as providing data-based constraints for theoreticians who are involved in modeling of the unusual electrical and electromechanical properties of undoped and doped ceria.

A review of defect structure and chemistry in ceria and its solid solutions

“…In these solid solutions, separately addressing the local environment around cerium and around the aliovalent dopant atoms is essential for understanding the macroscopic defect-related properties such as ionic conductivity, 3,134 electrostriction and anelasticity. 135 However, the absorption edges of different elements may be too close to each other so that their EXAFS spectra overlap, complicating analyses of both edges. Therefore, to take full advantage of the information contained in an EXAFS spectrum, the absorption edge (L I , L II or L III ) of Ce and Do must be chosen with care in order to separate them as much as possible.…”

“…15. Material properties reported in ceria in recent years, such as electrostriction and anelastic behavior 135 demonstrated that local strain fields may be active under applied anisotropic stress or electric field. As a result, advanced XANES and particularly EXAFS techniques were employed in order to observe changes in Cat-O distances in situ under an applied electric field.…”

“…Role of local strain fields in ceria mechanical and electromechanical properties. Some macroscopic properties of doped ceria, such as unusually large electrostrictive strain coefficients and room temperature anelastic behavior, 135 also support local deviation from fluorite symmetry, which produces anisotropic stress via reorganization of local dipolar strain fields.…”

“…This helped emphasize the role of defects when anisotropic stresses are applied to ceria materials, as summarized in a recent review. 135…”

Optical Analysis of Oxygen Self‐Diffusion in Ultrathin CeO2 Layers at Low Temperatures

“…In sum, the influence of strain to the oxygen diffusion in the CeO 2 coatings can be neglected, but grain boundary diffusion has to be considered besides the bulk diffusion process in the CeO 2 grains. Also, the anelastic properties of ceria might have influence on the oxygen penetration and diffusion properties in the ceria film and therefore on the determined diffusion coefficient and activation energy.…”