Electro-Mechanical Properties of Gadolinium Doped-Ceria Films Free of Mechanical Constraints

• Main Author: Mishuk, Eran
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Applied physics; Asymmetry; Bending stresses; Ceramics; Condensed matter physics; Crack initiation; Crystal structure; Deformation; Dielectric properties; Electric fields; Electrodes; Electrolytes; Electromagnetics; Electrostatic discharges; Ferroelectrics; Heat conductivity; Lasers; Materials science; Mechanics; Membranes; Metal fatigue; Microelectromechanical systems; Polymers; Scanning electron microscopy; Sensors; Spectrum analysis; Symmetry; Temperature; Thin films
• ISBN: 9798438788058
• DOI: 10.34933/wis.000510

This PhD thesis presents investigation of three issues related to non-classical electrostriction effect in thin films of gadolinium doped ceria (CGO): dependence of the electrostriction strain coefficient on frequency and magnitude of the electric field and mechanical fatigue in thin films. Electrostriction in CGO was first reported in 2012 for cantilever-shaped devices with substrate-clamped films. The current research focused on characterizing the electrostriction effect in self-supported films of CGO and have led to the following achievements: 1. Using silicon micro-fabrication processes, I successfully demonstrated actuation devices in the form of mm size membranes that display electromechanical actuation. The processes presented in this work provide a technological basis for integrating CGO as an active material in electro-active ceramic MEMS (microelectromechanical system)-devices. 2. Electro-mechanical measurements directly probed the electro-mechanical strain of CGO films, for the first time. The strain electrostriction coefficient was found to be in the order of 10-17 m2 ·V -2 . This value confirms previous findings that CGO displays non-classical electrostriction. 3. Frequency dependent measurements show, for the first time, that electrostriction in thin-films display Debye-like relaxation with frequency in the order of 60 - 170 mHz. These findings support the conjecture that the electrostriction in CGO originates from local elastic distortions, which comprise a few atoms (first cation coordination shell) that responds slowly to electric field. 4. I discovered that CGO films can display electro-chemo-mechanical (ECM) response, i.e. mechanical strain induced by change in the composition due to Faradaic processes. This is the first report on solid-state ECM actuation devices that work at room temperature. 5. Electro-thermal effect in membranes was used to facilitate the stability of CGO as an active component in MEMS actuation devices for the first time. Degradation in response was found to be primarily electrical in origin. Damage or mechanical fatigue was not found even after 107 actuation cycles at stress level which is ∼30% of the fracture strength of the membranes. The findings presented in this PhD thesis suggests that electrostrictive strain of self-supported films is related to the stress of clamped films only through the bulk (unrelaxed) elastic modulus (≈210 MPa). This is very surprising because at a few mHz frequency range CGO is strongly anelastic, meaning that stress and strain are linked via relaxed modulus (< 30 GPa). Therefore, comparison of the electrostriction effect with the anelasticity leads to the conclusion that the nature of the rearrangement of the local elastic dipoles, giving rise to both effects, is different.