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Electro-chemo-mechanical (ECM) coupling refers to mechanical deformation due to electrochemically driven compositional change in a solid. An ECM actuator producing micrometre-size displacements and long-term stability at room temperature was recently reported, comprising a 20 mol% Gd-doped ceria (20GDC), a solid electrolyte membrane, placed between two working bodies made of TiOx/20GDC (Ti-GDC) nanocomposites with Ti concentration of 38 mol%. The volumetric changes originating from oxidation or reduction in the local TiOx units are hypothesized to be the origin of mechanical deformation in the ECM actuator. Studying the Ti concentration-dependent structural changes in the Ti-GDC nanocomposites is therefore required for (i) understanding the mechanism of dimensional changes in the ECM actuator and (ii) maximizing the ECM response. Here, the systematic investigation of the local structure of the Ti and Ce ions in Ti-GDC over a broad range of Ti concentrations using synchrotron X-ray absorption spectroscopy and X-ray diffraction is reported. The main finding is that, depending on the Ti concentration, Ti atoms either form a cerium titanate or segregate into a TiO2 anatase-like phase. The transition region between these two regimes with Ti(IV) concentration between 19% and 57% contained strongly disordered TiOx units dispersed in 20GDC containing Ce(III) and Ce(IV) and hence rich with oxygen vacancies. As a result, this transition region is proposed to be the most advantageous for developing ECM-active materials. [ABSTRACT FROM AUTHOR]

Point defects such as oxygen vacancies and protonic interstitials are not only essential for ionic conductivity in oxides since they also affect the mechanical and electromechanical properties. These properties of nominally dry and hydrated proton‐conducting BaZr0.85M0.15O2.925+δH2δ (M = Al, Ga, Sc, In, Y, Eu) ceramics are investigated. Doping decreases Young's modulus with increasing ionic radii difference between the dopant and the host. Nominally dry samples show consistently higher Young's moduli than hydrated samples. All samples exhibit large non‐classical electrostriction, with a negative electrostriction coefficient M33<0. M33 shows saturation with the field and a non‐ideal Debye relaxation with frequency. The low‐frequency M33 value for both dry and hydrated samples shows a similar dependence on dopant radius as Young's modulus. For the hydrated samples, the relaxation frequency increases by a factor >100 in the series Ga‐Y, emphasizing the importance of proton trapping, with Y‐doped samples having minimal trapping energy. This coincides with the fact that the saturation strain for Y‐doped samples is also the smallest. In light of these findings, it is concluded that the present data give strong evidence for the existence of defect‐related elastic dipoles in acceptor doped barium zirconate and that the non‐classical electrostriction originates in their reorientation under electric field. [ABSTRACT FROM AUTHOR]

In functional materials, the local environment around active species that may contain just a few nearest‐neighboring atomic shells often changes in response to external conditions. Strong disorder in the local environment poses a challenge to commonly used extended X‐ray absorption fine structure (EXAFS) analysis. Furthermore, the dilute concentrations of absorbing atoms, small sample size and the constraints of the experimental setup often limit the utility of EXAFS for structural analysis. X‐ray absorption near‐edge structure (XANES) has been established as a good alternative method to provide local electronic and geometric information of materials. The pre‐edge region in the XANES spectra of metal compounds is a useful but relatively under‐utilized resource of information of the chemical composition and structural disorder in nano‐materials. This study explores two examples of materials in which the transition metal environment is either relatively symmetric or strongly asymmetric. In the former case, EXAFS results agree with those obtained from the pre‐edge XANES analysis, whereas in the latter case they are in a seeming contradiction. The two observations are reconciled by revisiting the limitations of EXAFS in the case of a strong, asymmetric bond length disorder, expected for mixed‐valence oxides, and emphasize the utility of the pre‐edge XANES analysis for detecting local heterogeneities in structural and compositional motifs. [ABSTRACT FROM AUTHOR]

Dimensional change in a solid due to electrochemically driven compositional change is termed electro‐chemo‐mechanical (ECM) coupling. This effect causes mechanical instability in Li‐ion batteries and solid oxide fuel cells. Nevertheless, it can generate considerable force and deformation, making it attractive for mechanical actuation. Here a Si‐compatible ECM actuator in the form of a 2 mm diameter membrane is demonstrated. Actuation results from oxygen ion transfer between two 0.1 µm thick Ti oxide\Ce0.8Gd0.2O1.9 nanocomposite layers separated by a 1.5 µm thick Ce0.8Gd0.2O1.9 solid electrolyte. The chemical reaction responsible for stress generation is electrochemical oxidation/reduction in the composites. Under ambient conditions, application of 5 V DC produces actuator response within seconds, generating vertical displacement of several µm with calculated stress ≈3.5 MPa. The membrane actuator preserves its final mechanical state for more than 1 h following voltage removal. These characteristics uniquely suit ECM actuators for room temperature applications in Si‐integrated microelectromechanical systems. [ABSTRACT FROM AUTHOR]

A noncontact displacement system suitable for tracking slow moving surfaces with low reflectivity is demonstrated. The displacement is measured by dynamic tracking of the moving focal plane of the sample under test. The system comprises a camera, a vertical digital piezo driver, and a data acquisition module. The tracking effect is achieved by continuously driving the sample with a 2-μm sweep around the focal plane, simultaneously acquiring the sample position and images of the part of the sample defined as a region of interest (ROI). The position of the focal plane is identified by fitting the contrast of the ROI versus the stage position to a Gaussian function. Using an ROI provides the ability to test various regions across the object and eliminates the demand for the surface to be flat or reflective. The system is low cost, is applicable to a large variety of samples and has an accuracy better than 10 nm. [ABSTRACT FROM AUTHOR]

Gd‐doped ceria (CGO), one of the most extensively studied oxygen ion conductors, is a low dielectric constant/low mechanical compliance material exhibiting large nonclassical electrostriction. The electromechanical response of the micro‐electromechanical devices with CGO films as an active material described previously can not be attributed exclusively to electrostriction. Here it is shown that, below 1 Hz, in addition to electrostriction (second‐harmonic response), there is a strong contribution of the electro‐chemomechanical effect (ECM, first harmonic response). ECM is the change in mechanical dimensions of ionic and mixed ionic‐electronic conductors as a result of a change in chemical composition induced by an electric field. In batteries, the presence of ECM is highly detrimental. In ceria at room temperature, it was considered to be negligible because of slow oxygen diffusion. This work demonstrates ECM actuation at ambient temperature and moderate electric field (<5 V µm−1). ECM‐induced strain is attributed to reversible oxidation/ reduction of TiO2 layers at the Ti‐CGO interface. At 25 °C, the ECM bending strain is 1.2 × 10−6, increasing exponentially with temperature. These data suggest that with a proper choice of materials, ECM‐type response can be a viable mechanism for mechanical actuation at ambient and also at slightly elevated temperatures. Electromechanical response of Al/Ti/Ce0.8Gd0.2O1.9/Ti/Al structure consists of two contributions: electrostriction at the second harmonic (top panel), which involves in‐plane expansion, and the electro‐chemomechanical effect at the first harmonic (bottom panel), which originates from oxidation/reduction of Ti at the Ce0.8Gd0.2O1.9/Ti interface. [ABSTRACT FROM AUTHOR]

In article number 1804433, Olga Kraynis, Igor Lubomirsky, and co‐workers evaluate Raman spectroscopy as a characterization tool for anisotropic strain in lanthanide‐doped ceria films. The effective Grüneisen parameter, obtained by comparing substrate‐supported vs. self‐supported membranes, turns out to be 30% lower than its equivalent for bulk material. This suggests defect‐related properties play a major role when characterizing the strain of ceria‐based devices. [ABSTRACT FROM AUTHOR]

A protocol for characterizing relaxation of anisotropic strain in thin films of 10 mol% Eu‐ or Sm‐doped ceria is described. The method is based on comparison of Raman spectra and X‐ray diffraction patterns from substrate‐supported films, displaying in‐plane compressive strain (initial state), with analogous data from 2 mm diameter self‐supported films (i.e., membranes), prepared by partial substrate removal (final state). These membranes are found to be relaxed, i.e., approximately unstrained, but with increased unit cell volume. The effective (i.e., 2‐state) Grüneisen parameter of the F2g Raman active mode for these films is calculated to be 0.4 ± 0.1, which is ≈30% of the literature value for the corresponding ceramics under isostatic pressure. On this basis, it is found that the observed red‐shift of the F2g mode frequency following isothermal strain relaxation of the doped ceria thin films cannot be determined solely by the increase in average unit cell volume. The study presented here may shed light on the suitability of Raman spectroscopy as a technique for characterizing strain in lanthanide‐doped ceria thin films. Raman mode‐Grüneisen parameters are often used to assess strain in thin films. The Raman F2g mode‐Grüneisen parameter measured for thin films of Eu‐ and Sm‐doped ceria is ≈30% of the literature value for the corresponding ceramics under isostatic pressure. This discrepancy is attributed to defect‐related properties of Eu‐ and Sm‐doped ceria. [ABSTRACT FROM AUTHOR]

Electro-chemo-mechanical (ECM) coupling refers to mechanical deformation due to electrochemically driven compositional change in a solid. An ECM actuator producing micrometre-size displacements and long-term stability at room temperature was recently reported, comprising a 20 mol% Gd-doped ceria (20GDC), a solid electrolyte membrane, placed between two working bodies made of TiO x /20GDC (Ti-GDC) nanocomposites with Ti concentration of 38 mol%. The volumetric changes originating from oxidation or reduction in the local TiO x units are hypothesized to be the origin of mechanical deformation in the ECM actuator. Studying the Ti concentration-dependent structural changes in the Ti-GDC nanocomposites is therefore required for (i) understanding the mechanism of dimensional changes in the ECM actuator and (ii) maximizing the ECM response. Here, the systematic investigation of the local structure of the Ti and Ce ions in Ti-GDC over a broad range of Ti concentrations using synchrotron X-ray absorption spectroscopy and X-ray diffraction is reported. The main finding is that, depending on the Ti concentration, Ti atoms either form a cerium titanate or segregate into a TiO 2 anatase-like phase. The transition region between these two regimes with Ti(IV) concentration between 19% and 57% contained strongly disordered TiO x units dispersed in 20GDC containing Ce(III) and Ce(IV) and hence rich with oxygen vacancies. As a result, this transition region is proposed to be the most advantageous for developing ECM-active materials., (open access.)

Symmetry-imposed restrictions on the number of available pyroelectric and piezoelectric materials remain a major limitation as 22 out of 32 crystallographic material classes exhibit neither pyroelectricity nor piezoelectricity. Yet, by breaking the lattice symmetry it is possible to circumvent this limitation. Here, using a unique technique for measuring transient currents upon rapid heating, direct experimental evidence is provided that despite the fact that bulk SrTiO 3 is not pyroelectric, the (100) surface of TiO 2 -terminated SrTiO 3 is intrinsically pyroelectric at room temperature. The pyroelectric layer is found to be ≈1 nm thick and, surprisingly, its polarization is comparable with that of strongly polar materials such as BaTiO 3 . The pyroelectric effect can be tuned ON/OFF by the formation or removal of a nanometric SiO 2 layer. Using density functional theory, the pyroelectricity is found to be a result of polar surface relaxation, which can be suppressed by varying the lattice symmetry breaking using a SiO 2 capping layer. The observation of pyroelectricity emerging at the SrTiO 3 surface also implies that it is intrinsically piezoelectric. These findings may pave the way for observing and tailoring piezo- and pyroelectricity in any material through appropriate breaking of symmetry at surfaces and artificial nanostructures such as heterointerfaces and superlattices., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)