Research On The Mechanical Behavior Of Solid Electrolyte Under The Coupled Mechanical And Electrochemical Fields

With the increasingly severe environmental pollution and energy shortage, solidoxide fuel cells (SOFCs) have attracted extensive attention for their high powerefficiency and low pollution. However, the widespread commercialization of SOFCs isimpeded by some undeveloped technologies, especially the development of a solidelectrolyte material with a sufficient mechanical strength and a high ionic conductivityat working temperatures. By doping the gadolinia during the synthesis process, someoxygen vacancies are generated to promote ionic conductivity. However, the mechanicalproperties of the solid electrolyte materials are severely attenuated by introduced pointdefects. The conductivity of oxygen is influenced by the deformation behaviorreciprocally. In this thesis, molecular dynamics simulations were conducted on theuniaxial tensile behavior and diffusion behavior of gadolinia doped ceria (GDC). Themechanical behavior of GDC was studied systematically from microscopic view. Theinfluences of several factors on the mechanical properties were analyzed too.First, the basic principles of molecular dynamics were introduced. Based on them,the project of molecular dynamics simulation of uniaxial tension was formulated. TheGDC models with different defect concentrations were made by manipulating thedoping content. Then, the simulations of GDC with different defect concentrations atdifferent temperatures were accomplished. The GDC is observed to undergo astress-induced martensitic phase trnasformation from a fluorite structure to a rutilestructure or its twin structure by considering the atomic configurations and the statisticdata of the simulation processes. The mechanism and the classification were discussed.Secondly, it is found that the addition of point defects has a significant influence onthe phase transformation behavior of GDC, which limits the further deformation and theloading capacity of the material. The influences were explained with considering theformer analysis. The dopant-dependent tensile strength is obtained and is observed to beconsistent with reported experimental measurements.Finally, the diffusion behavior of the oxygen ions in GDCs was simulated by usingmolecular dynamics. With the computation and comparison the diffusion coefficients ofoxygen ions in GDCs, strain and martensitic phase transformation on the diffusionbehavior were obtained. And the mechanisms of the influences were analyzed from the microscopic view.