Locally concentrated protons control the proton diffusivity in heavily Sc-doped perovskites

Journal article, 2026

Proton-conducting perovskites with heavy acceptor doping exhibit promising proton conductivity at intermediate-to-low temperatures. However, the understanding of how the high concentration of protons interacts with the local structure of dopants and the consequent effects on proton diffusivity remains insufficient. In this study, we combine in situ and isotope exchange Raman spectroscopy with neutron total scattering to investigate the effects of local structure and high proton concentration on proton diffusivity in BaSc1–x Mo x O2.5+3x/2 (BSM). BSM exhibits high bulk proton conductivity of above 0.01 S cm^–1 at 350 °C. However, in BSM with higher Sc and proton concentrations, the proton diffusivity is reduced. Neutron pair distribution analysis reveals that the energetically preferred proton sites are located around ScO6 octahedra. The locally concentrated protons lead to the carrier blocking effect, which predominantly restricts proton diffusion by decreasing the pre-exponential factor. Furthermore, the localized protons induce greater local lattice asymmetry, further impeding proton transport. The results indicate a critical trade-off between localized proton concentration and proton diffusivity in metal oxides. This study highlights the importance of considering local structure, in addition to long-range crystal structure, to understand proton transport properties in heavily doped perovskites. Our findings suggest optimization strategies for heavily acceptor-doped proton-conducting ceramics by using lower-valence B-site elements.