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Solid oxide fuel cells (SOFCs) directly convert chemical to electrical energy with high efficiency and can operate using a wide variety of fuels ranging from hydrogen and kerosene to gasified coal [1] [2] . Many of the more advanced oxides utilized in SOFCs experience significant changes in oxygen content, or oxygen stoichiometry, during operation, resulting in changes in volume and elastic properties termed chemomechanics [3] [4] . This lattice dilation known as chemical expansion, analogous to temperature induced thermal expansion, is oxygen nonstoichiometry-induced and can cause large stress gradients across a SOFC stack, with potential for negative impact on device performance [5] . Therefore, a fundamental understanding regarding the coupling between solid-state electrochemistry and mechanical deformation is required for successful development of functionally superior and long-lived fuel cell systems. In this project, we are studying the chemical expansion coefficient, elastic properties, and oxygen stoichiometry of thin film and bulk SOFC oxide materials. Thin films are of particular interest since they allow control of strain and increase the surface-to-volume ratio, particularly important for electrode performance. Furthermore, there is a trend towards the use of thinner structures such as m-SOFCs [6] . The chemomechanical properties are being investigated using high temperature and atmosphere-controlled nanoindentation, high-resolution x-ray diffraction, dilatometry, impedance spectroscopy, and thermo-gravimetry techniques.
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