31.01.14 KB. Ok to add accepted version to spiral, embargo period expired

3YSZ green layers approximately 10 μm thick were screen printed onto 3YSZ substrates up to 300 μm in thickness. The stress induced by constrained sintering of the film (between 1150° and 1350°C) was measured by monitoring the bending displacement of vertical strips of bilayers using a long‐distance microscope. In order to deduce the stress it was first necessary to measure the creep properties of the substrates by monitoring the bending of horizontal beams under gravity. The creep strain rate of the 3YSZ substrates was linearly dependent on applied stress at the low stresses and strains involved in the present work. The creep viscosity appeared to increase with strain (time), which might be due to changes in grain‐boundary composition, and had higher activation energy at temperatures above approximately 1250°C. The magnitudes of the creep viscosities are in reasonable agreement with other creep data in the literature for 3YSZ. The in‐plane stress induced during constrained sintering of the 3YSZ films had a maximum value of approximately 3 MPa at 1200°C. This behavior is consistent with literature results reported for constrained sintering of bulk alumina. The stress induced by the constraint is of a similar order to the estimated sintering potential.

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In some planar SOFCs a thin film electrolyte is sintered onto a "rigid" substrate which constrains the film so that it can shrink only in one dimension, i.e. perpendicular to the substrate. The resulting stress and its effects on sintering kinetics and microstructure have been measured for screen printed YSZ films. The stress is in the range 0.5 to 3 MPa, depending on sintering temperature. The constraint slows the densification rate dramatically and results in porous defects that can compromise the gas-tightness of an electrolyte film.