www.advmatinterfaces.de FULL PAPER 1801592 (1 of 9) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Electro-chemomechanical Contribution to Mechanical Actuation in Gd-Doped Ceria Membranes Eran Mishuk, Andrei Ushakov, Evgeniy Makagon, Sidney R. Cohen, Ellen Wachtel, Tanmoy Paul, Yoed Tsur, Vladimir Ya. Shur, Andrei Kholkin,* and Igor Lubomirsky* DOI: 10.1002/admi.201801592 δ - phase Bi 2 O 3 . [8] Thin films of CGO are not difficult to deposit and, as has been demonstrated, they can be incorporated into Si-based devices using standard micro-machining processes. [9–12] To date, the electrostriction effect in CGO has mainly been studied in the frame- work of substrate supported films or ceramics. [6,7,13–15] Previously, we have demonstrated the feasibility of mechanical actuation with CGO-based devices and have shown that the choice of contact metal is critical for functionality. [12,14,16] Of the electrodes tested, titanium contacts were found to display the lowest resistance. [12,16] How- ever, the electromechanical response of micro-electromechanical systems (MEMS) based on CGO films was found to be com- plex. [12] This complexity has two sources. i) CGO is strongly anelastic. [9,10,17,18] The frequency range of the anelasticity (<0.5 Hz) clearly overlaps the frequency range within which nonclassical elec- trostriction is observed, [6,13,15] making precise identification of the nature of the response difficult. ii) CGO is one of the best oxygen ion con- ductors. Therefore, electrochemical oxygen exchange reactions at the interface with a titanium electrode is possible even at room temperature. These electrochemical reactions may induce electro-chemomechanical (ECM) response, i.e., mechanical deformation induced by electrochemically driven changes in composition. [19–21] Therefore, ECM and electrostrictive responses may superimpose. 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 TiO 2 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. E. Mishuk, E. Makagon, Dr. E. Wachtel, Prof. I. Lubomirsky Department of Materials and Interfaces Weizmann Institute of Science Herzl St 234, Rehovot 7610001, Israel E-mail: Igor.Lubomirsky@weizmann.ac.il A. Ushakov, Prof. V. Ya. Shur, Prof. A. Kholkin School of Natural Sciences and Mathematics Ural Federal University Lenin Ave. 51, Ekaterinburg 620000, Russia E-mail: kholkin@ua.pt Electro-Chemomechanical Actuation 1. Introduction Gd-doped ceria (CGO) is one of the most extensively studied ionic conductors, finding application in a variety of fields ranging from fuel cells to memristors. [1–4] Recently, CGO was reported to exhibit large non-classical (non-Newnham) electrostric- tion. [5–7] This report was followed by the demonstration of non-classical electrostriction in ceramics of (Nb, Y)-stabilized Dr. S. R. Cohen Department of Chemical Research Support Weizmann Institute of Science Herzl St 234, Rehovot 7610001, Israel Dr. T. Paul, Prof Y. Tsur Department of Chemical Engineering and the Grand Technion Energy Program Technion-Israel Institute of Technology Haifa 3200003, Israel Prof. A. Kholkin Department of Physics and CICECO-Aveiro Institute of Materials University of Aveiro 3810-193 Aveiro, Portugal The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/admi.201801592. Adv. Mater. Interfaces 2019, 1801592