Abstract
Experimental studies have found a giant electrostriction effect in gadolinium-doped ceria (GDC) despite its low permittivity. This unique phenomenon has been linked to the presence of overcompensating vacancies and to the occurrence of a phase transition, implying an abrupt change in cation-oxygen bond distance. In this study, we have used computational methods based on density functional theory and on interatomic potentials to help understand the mechanism of the electrostriction effect in GDC. By combining these two methods, we obtained the lowest-energy configurations of Ce1−xGdxO2−x/2 in the entire range of x. Our results suggest that no ordinary phase transition exists as a function of the composition. However, the atomic rearrangements that occur as the concentration of vacancies and dopants increases cause an abrupt change in cation-oxygen bond distance that could be responsible for the electrostrictive properties of GDC.
Highlights
Films, a material with a dielectric constant of just around 30
Li et al.9 studied the local distortions in gadolinium-doped ceria (GDC) by using X-ray absorption and fluorescence detection, and they stated that when electric fields are applied, there are atomic rearrangements that might be relevant for the giant electrostriction observed
The availability of different configurations with similar energy but different vacancy ordering at around x = 0.25 would explain why the action of an external electric field would allow for dramatic changes in the structural properties of the material, giving rise to a large electrostriction effect—this vacancy mobility in GDC is not surprising, given that it is a well known ionic conductor
Summary
Films, a material with a dielectric constant of just around 30. In this case, the electrostriction coefficient that relates stress σ to the square of the electric field E (σ = YME2, where Y is the Young’s modulus) is around M = 6 × 10−18 m2/V2, which is to be compared to the one of a typical material with a similar dielectric constant such as MgO (M = 2 × 10−21 m2/V2) and to the one of a good electrostrictor such as Ca-doped PMN (M = 3.5 × 10−21 m2/V2, dielectric constant of 4000).4. This offers a first possibility for saving computing time when studying the energetics of different arrangements (filtering criteria): the energies of configurations where the atoms with identical lists of neighbor distances are assumed to be the same.
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