Ferroelastic properties in cubic Sm doped ceria

Ferroelasticity is characterized by a hysteresis loop in the strain-stress dependence of the material. The hysteresis in strain upon application of external stress is enabled by mechanical switching between at least two orientation states of the crystal, i.e., non-cubic structure. In strain glass, the material contains small regions or domains with lower symmetry compared to the material`s average symmetry. This means that in contrast to ferroelastic material, even materials with average cubic symmetry can be in a strain glass state. Similarly to the ferroelastic case, the elastic domains in a strained glass can be orientated. Unlike the ferroelastic case, the process strongly depends on frequency, material history and does not change the average material symmetry.

In the last decade, oxygen ion conductors of the fluorite symmetry, such as doped ceria RE_xCe_1-xO_2-x/2 (RE= Rare Earth, e.g., Gd, Sm, etc.), were found to exhibit strong anelastic effects. These observed effects include room temperature creep and time dependence of elastic moduli. Moreover, these materials exhibit a strong second-order electro-mechanical response (electrostriction). It was suggested that these effects are correlated with elastic domains, which form in high concentrations (>1%) of oxygen vacancies.

In this presentation I show that Sm doped ceria presents a hysteresis loop under mechanical stress. Additionally, under DC electric field the material expands and does not recover upon electric field removal. However, the material regains its original dimensions after heating to about 140 °C. These hysteresis strain behaviors suggest that doped ceria may be classified as ‘strain glasses’.