Electromechanically active pairs dynamics in Gd-doped ceria single crystal

Oxygen defective ceria, e.g. Gd-doped ceria, shows giant electromechanical properties related to a complex local rearrangement of its lattice. Although they are not entirely identified, the electroactive mechanisms arise from cations and oxygen vacancies (V_O) pairs (Ce-V_O), and the local structural elastic distortion in their surroundings. Here, we study the geometry and behaviour of Ce-Vo pairs in a grain boundaries-free bulk Ce_0.9Gd_0.1O_1.95 single crystal under an AC electric field of ca. 11 kV/cm. The analysis was carried out through X-ray absorption spectroscopy (XAS) techniques at Ce L-III edge. Using Density Functional Theory (DFT) calculations, we investigated the effects of the strain on states' density and orbitals at the valence band edge. Our research indicates that the electrostriction increases at low temperatures. The electromechanical strain has a structural nature and can rise of one order of magnitude, i.e., from 5·10^-4 at room temperature to 5·10^-3 at -193 °C, due to an increase in the population of the electrically active pairs. At a constant VO concentration, the material can thus configure heterogeneous pairs and elastic nanodomains that are either mechanically responsive or not.