Proton incorporation behavior into grain boundaries of YSZ and GDC

Abstract The deuteron incorporation behavior of 8YSZ and 10GDC polycrystals was investigated using secondary ion mass spectrometry (SIMS). As a result of the deuteron solubility measurements of 10GDC polycrystals, the solubilities were found to increase with increasing grain boundary densities. This indicated that deuterons are incorporated mainly into the grain boundaries, which agrees with the finding of our recent study on 8YSZ. It was also observed that the deuteron solubilities in both materials increased with decreasing temperature and showed the opposite relationship with D2O vapor pressure (pD2O). This suggested that deuterons are incorporated into the grain boundaries by the reaction of D2O vapor with the oxygen vacancies, as is the case in perovskite-type proton conductors. However, the expected linear relationship between the solubilities and pD2O1/2, which was theoretically derived from the suggested incorporation reaction, was not observed. Based on the trapping model, this discrepancy is attributed to the existence of two types of deuterons with different incorporation energies. The determined hydration enthalpies for trap-free and trapping sites at the grain boundaries were − 33 and − 184 kJ mol−1 for 8YSZ, and − 47 and − 160 kJ mol−1 for 10GDC, which were in good agreement with the reported hydration enthalpies for the perovskites.