Thermal expansion and elastic moduli of electrolyte materials for high and intermediate temperature solid oxide fuel cell

The development of thermal stresses in solid oxide fuel cells (SOFCs), and thus their structural stability and reliability, depends directly on the thermal expansion and elastic moduli of the constituent materials. Therefore, it is important to study these properties of SOFC materials. In this study, the thermal expansion and elastic properties of common electrolyte materials, namely yttria stabilized zirconia (YSZ), scandia and ceria stabilized zirconia (SCSZ) and gadolinia doped ceria (GDC), are reported. High temperature X-ray diffraction (HT-XRD) was used to show that the cubic structure of YSZ and GDC samples is stable throughout the temperature range of 30-800 °C. However, SCSZ undergoes partial cubic to rhombohedral phase transition at around 300 °C but transferred completely back to cubic phase at around 500 °C upon heating. The coefficient of thermal expansion (CTE) of electrolyte materials was measured using thermo-mechanical analyzer (TMA). It was found that the CTE of SCSZ is almost identical to that of YSZ, but lower than that of GDC. Elastic properties (Young's and shear moduli) were determined in the 25-900 °C temperature range using resonant ultrasound spectroscopy (RUS). Young's and shear moduli of GDC decrease almost linearly with temperature, with an exception of the small anomaly between 100 °C and 300 °C. However, the variation of elastic moduli with temperature was found to be highly non-linear for YSZ and SCSZ with minimum values measured at around 600 °C. The deviation from the linear decrease of elastic moduli with increasing temperature is related to the relaxation of oxygen vacancy complexes and phase transformations.