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Ceria based electro-chemo-mechanical actuator with Ti/Ce_1-xGd_xO_2-x/2 cermet contacts

The chemo-mechanical effect in a solid refers to dimensional change due to change in stoichiometry ^[1]. Dimensional change caused by compositional change induced by an electric field has been termed the electro-chemo-mechanical (ECM) effect. Such instability is clearly deleterious for batteries or fuel cells, but, as recently suggested, has potential for use in actuation ^[2]. The structure of a typical actuator device that operates on the ECM principle is a micrometer thick solid electrolyte (SE) sandwiched between two ECM-active layers. An electrochemical reaction must occur in these layers, causing them to expand or contract. In order to facilitate the ECM response, these layers must have mixed ionic and electronic conductivity (MIEC) and a large chemical expansion coefficient.

We have constructed a room temperature self-supported, thin film, ECM actuator with Gd doped CeO₂ (GDC) as the SE. We have tested two alternatives for the active layers: (a) a single phase metal/metal oxide layer ^[3] ; and (b) GDC/nanocrystalline metal cermet. Electrical and electromechanical measurements demonstrated that the metal/metal oxide actuator response is limited by the rate of oxygen diffusion from the SE to the metal surface. Actuators with cermet active layers provide better MIEC and larger vertical displacement (>1.5μm).

[1] S. R. Bishop, D. Marrocchelli, C. Chatzichristodoulou, N. H. Perry, M. B. Mogensen, H. L. Tuller, E. D. Wachsman, Annu Rev Mater Res 2014, 44, 205-239.

[2] J. G. Swallow, J. J. Kim, J. M. Maloney, D. Chen, J. F. Smith, S. R. Bishop, H. L. Tuller, K. J. Van Vliet, Nat Mater 2017, 16, 749-+.

[3] E. Mishuk, E. Makagon, E. Wachtel, S. R. Cohen, R. Popovitz-Biro, I. Lubomirsky, Sensor Actuat a-Phys 2017, 264, 333-340.