Bulk protons in anhydrous perovskites—neutron scattering studies

• Ba- and Sr-based zirconate ceramics—good proton conductors, were investigated using TOF neutron spectrometer.
• Elastic scattering revealed low content of bulk protons.
• The highest local proton motion is detected near 500 °C.
• The inelastic neutron spectra reveal a free nature of bulk proton.

Thanks to their high proton conductivity at medium temperature, perovskite ceramics are promising electrolytic membranes of fuel cells, water steam electrolysers and CO2/syngas converters. Prior to such applications, some important aspects need to be clarified: (i) the real content of bulk protons, (ii) the optimum temperature range of proton dynamics and (iii) the true proton nature. Neutron scattering experiments appear especially well suited to study these aspects. Consequently, we performed quasi-elastic (QENS) and inelastic (INS) neutron scattering experiments on highly dense MZr0;9Yb0.1O3-δ (M: Sr or Ba) ceramics using a time-of-flight spectrometer (MIBEMOL) at the Léon Brillouin Laboratory (Saclay, France). The results show that very low bulk proton content, i.e., 2–4.5 × 10− 3 mol/mol, in the case of SrZr0.9Yb0.1O3-δ ceramics gives rise to maximum of mean square displacement (MSD) near 500 °C. The comparison of inelastic spectra recorded for protonated and non-protonated BaZr0.9Yb0.1O3-δ and SrZr0.9Yb0.1O3-δ confirms our previous IR results revealing the free nature of the bulk protons.