Anelastic and Electromechanical Properties of Doped and Reduced Ceria

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.