Elastic dipole alignment is the origin of anelasticity and electrostriction in aliovalent-doped ceria

We investigated the nature of recently discovered anelasticity and electrostriction in aliovalent ceria. DC bias ≤10 kV/cm was applied to trivalent-doped ceria ceramics. ∼20 nm thick TaO_x was used as a blocking layer at the Ta electrode/ceramic interface. Strain was monitored in situ with X-ray diffraction and X-ray absorption spectroscopy. The electric field produces out-of-plane tensile strain ≤ 1200 ppm near the positive electrode. Upon field removal, strain persists for ≥ 24 h at 300 K but is fully reversible following 5 h at 413 K. The positive strain is not due to compositional change; rather, it is anelastic residual strain, confirming the existence of elastic dipoles. From the dopant concentration dependence of the saturation strain, the elastic dipole extent is estimated to be ∼1.9 unit cells. Density functional theory (DFT) calculations predict the formation of extended elastic dipoles due to interacting oxygen vacancies and trivalent dopants. Combining DFT and molecular dynamics (MD) simulations, we offer a model that explains key experimental observations: absence of zero-field elastic dipole; contraction in the direction of the electric field on a time scale ≤ 4 s; and large expansion in the DC electric field after 14 h. The proposed model may describe anelasticity and electrostriction in other ionic conductors where they originate from dopant-vacancy induced elastic dipoles.