In order to make correct statements about the role of protons and oxygen vacancies on the structure and dynamics of proton-conducting oxides, an accurate measure of the proton concentration in the material is necessary. Determinations of proton concentrations are done routinely using thermogravimetric methods by measuring the weight change of the sample during dehydration on heating [26]. However, the use of thermogravimetric methods is not suitable for all types of materials. For example, hydrated perovskites containing elements that may change oxidation state upon heating may decrease in mass because of oxygen loss in addition to the evaporation of water molecules. An alternative technique for the analysis of proton concentration in such systems is neutron prompt-gamma activation analysis (PGAA), which can indeed be used for determining the presence and amount of elements in materials, irrespective of oxidation state.

An example of a PGAA study of a proton-conducting perovskite is the work by Jones et al. [75] on undoped and Y-doped BaPrO3. The PGAA spectra of dry and hydrated (saturated) BaY01Pr0.9O3_,5 are shown in Fig. 9.12a. The sensitivity to hydrogen and the effect of hydration are clearly visible. The proton concentration,

as derived from the PGAA spectra, is shown in Fig. 9.12b for both samples. A key result of this study is that the proton concentration in the hydrated Y-doped BaPrO3 sample is as much as three times larger than the dopant concentration. The unex- pectedly-high proton concentration in the hydrated sample is thought to occur as a result of the change of the Pr oxidation state from +4 to +3. This implies that the Pr ions act as self-dopants, which form intrinsic oxygen-vacancies that add to the oxygen vacancies formed by the replacement of Pr for Y. Hence, the material can accommodate more — OH groups and therefore take up more protons than is expected from the dopant concentration alone. This information is naturally of paramount importance for making the correct analysis and conclusions from data obtained in both structural and dynamical studies.