Electrostriction is the upsurge of strain under an electric field in any dielectric material. Oxygen-defective metal oxides, such as acceptor-doped ceria, exhibit high electrostriction 10-17 m2V-2 values, which can be further enhanced via interface engineering at the nanoscale. This effect in ceria is "non-classical" as it arises from an intricate relation between defect-induced polarisation and local elastic distortion in the lattice. Here, we investigate the impact of mismatch strain when epitaxial Gd-doped CeO2 thin films are grown on various single-crystal substrates. We demonstrate that varying the compressive and tensile strain can fine-tune the electromechanical response. The electrostriction coefficients achieve a large M11 ≈ 3.6·10-15 m2V-2 in lattices of in-plane compressed films, i.e., a positive tetragonality (c/a-1 > 0), with stress above 3 GPa at the film/substrate interface. Chemical and structural analysis suggests that the high electrostriction stems from anisotropic distortions in the local lattice strain, which lead to constructively oriented elastic dipoles and Ce3+ electronic defects. Non-classical electrostriction in fluorites arises from defect-induced polarization and lattice distortions. This study shows that mismatch strain in Gd-doped CeO2 thin films fine-tunes electromechanical responses, achieving high electrostriction above 10−15 m2V−2.

Oxygen-defective metal oxides, e.g., acceptor-doped CeO2, demonstrate exceptionally large electrostrictive responses compared to state-of-the-art electromechanically active ceramic materials.

Electrostriction is a property of dielectric materials whereby an applied electric field induces a mechanical deformation proportional to the square of that field. The magnitude of the effect is usually minuscule (<10 –19 m 2 V –2 for simple oxides). However, symmetry-breaking phenomena at the interfaces can offer an efficient strategy for the design of new properties 1 , 2 . Here we report an engineered electrostrictive effect via the epitaxial deposition of alternating layers of Gd 2 O 3 -doped CeO 2 and Er 2 O 3 -stabilized δ-Bi 2 O 3 with atomically controlled interfaces on NdGaO 3 substrates. The value of the electrostriction coefficient achieved is 2.38 × 10 –14 m 2 V –2 , exceeding the best known relaxor ferroelectrics by three orders of magnitude. Our theoretical calculations indicate that this greatly enhanced electrostriction arises from coherent strain imparted by interfacial lattice discontinuity. These artificial heterostructures open a new avenue for the design and manipulation of electrostrictive materials and devices for nano/micro actuation and cutting-edge sensors.

Electrostriction materials are used in the industry and research as transducers in low dimensional systems such as micro-pumps and micro-electromechanical systems (MEMS). Thanks to the high actuation accuracy and lack of hysteresis, they are preferred to piezoelectric materials as thin films. Many kinds of materials show high electrostriction activity, and their variety is a crucial advantage for the development of lead-free transducers. This chapter describes the properties and performances of oxide electrostrictors, particularly Gd-doped CeO 2 . We analyze the unusually high electrostriction effect for oxygen vacancies interaction in the lattice. Finally, we highlight the characteristics of microactuator systems such as thin films and free-standing membranes.

A new functional carbon–metal oxide hybrid is designed and fabricated by field-assisted sintering—the hybrid material results in enhanced electro-chemo-mechanical properties with high crystallinity, facile fabrication method, and cost-efficiency.

To maximize the synergistic effects of hybridized heteromaterials in terms of device performance of piezoelectric nanogenerators (PNGs), we demonstrate an unprecedented strategy for the direct growth of perovskite piezoelectric barium titanate (BTO) nanoparticles (NPs) on two-dimensional graphene oxide (GO) via a simple hydrothermal method. The mutual interactions between the strongly coupled heteromaterials in terms of their structural, chemical, and electrical variations are systematically explored. From these comprehensive spectroscopic and microscopic examinations, we ascertain that the hybridization of BTO NPs with GO enables to enhance the piezoelectric response of the PNGs compared with those of pristine BTO NPs-based PNGs and simply mixed BTO NPs/GO-based PNGs. This can be understood by the synergistic interplay of the heteromaterials associated with (i) the formation of homogeneous size distribution of the BTO NPs after the hybridization, (ii) healing of oxygen vacancies in the BTO crystals and a simultaneous improvement in the crystallinity of GO through chemical reduction.

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 cation and oxygen vacancy (VO) pairs (i.e. Ce-VO), and the local structural elastic distortion in their surroundings. Here, we study the geometry and behaviour of Ce-VO pairs in a grain boundary-free bulk Ce0.9Gd0.1O1.95 single crystal under an AC electric field of ca. 11 kV cm-1. The analysis was carried out through X-ray absorption spectroscopy (XAS) techniques at the Ce L-III edge. Using Density Functional Theory (DFT) calculations, we investigated the effects of the strain on density of states and orbitals at the valence band edge. Our research indicates that electrostriction increases at low temperatures. The electromechanical strain has a structural nature and can rise by 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.

Since the discovery of ferroelectric electrostrictive ceramics such as Pb(Mg1/3Nb2/3)O3 (PMN) in 1980 and following inclusion of other kind of materials (linear dielectrics, glass ceramics, defective oxides), electrostriction effect has been focus of much attention of research and industry with a succession of new field of development and commercial application. While piezoelectricity remains a "competitor," electrostrictive ceramics set aside a market in low dimensional application such as micro-pumps, positioning and micro-electromechanical systems (MEMS). Also the heterogeneous variety of electrostrictors materials is a crucial point on the development of lead-free transducer. In this work, we describe the basics of the electrostriction effect, in both microscopic and macroscopic points of view. We highlight the most relevant applications and we analyze the different families of electrostrictive compounds.

Enhanced Gd-doped ceria electrostriction: This study uncovers new anisotropic properties in thin films, enhancing the effect along with the 〈100〉 directions by one order of magnitude and proposing a new microscopic model to explain such findings.

Recent investigations have shown that highly oxygen defective cerium oxides generate non-classical electrostriction that is superior to lead-based ferroelectrics. In this work, we report the effect of field-assisted spark plasma sintering (SPS) on electro-chemo-mechanical properties on Ca-doped ceria (CDC). Nanometric powders of ca. 10 nm are rapidly consolidated to form polycrystalline nanostructures with a high degree of crystalline disorder. Remarkably, the resultant material demonstrates a large electromechanical strain without a frequency-related relaxation effect. We conclude that electromechanical activity in CDC materials strictly depends on the Ca-VO interaction, while disorder at the crystalline boundaries has a minor effect.

Atomic-scale simulations identify the substitutional chemistry of cerium oxide beyond the trivalent, rare-earth cations.

Gadolium doped ceria, Gd:CeO2 (CGO), have recently been shown to possess an exceptional high electrostriction coefficient (Q), which is at the least three orders of magnitude larger than the best performing lead-based electrostrictors, e.g. Pb(Mn1/3Nb2/3)O3. Herein, we show that CGO thin films fabricated by a pulsed laser deposition method can be directly integrated onto the Si substrate by using TiN films of few nanometers as functional electrodes. The exceptional good coupling between TiN and Ce0.8Gd0.2O1.9 yields a high electrostriction coefficient of Qe = 40 m4 C−2 and a superior electrochemomechanical stability with respect to the metal electrodes.

Some oxygen defective metal oxides, such as cerium and bismuth oxides, have recently shown exceptional electrostrictive properties that are even superior to the best performing lead-based electrostrictors, e.g. lead-magnesium-niobates (PMN). Compared to piezoelectric ceramics, electromechanical mechanisms of such materials do not depend on crystalline symmetry, but on the concentration of oxygen vacancy in the lattice. In this work, we investigate for the first time the role of oxygen defect configuration on the electro-chemo-mechanical properties. This is achieved by tuning the oxygen defects blocking barrier density in polycrystalline gadolinium doped ceria with known oxygen vacancy concentration, Ce0.9Gd0.1O2-x,x= 0.05. Nanometric starting powders of ca. 12 nm are sintered in different conditions, including field assisted spark plasma sintering (SPS), fast firing and conventional method at high temperatures. These approaches allow controlling grain size and Gd-dopant diffusion, i.e. via thermally driven solute drag mechanism. By correlating the electro-chemo-mechanical properties, we show that oxygen vacancy distribution in the materials play a key role in ceria electrostriction, overcoming the expected contributions from grain size and dopant concentration.