Hydrogen dynamics features in BaZr1 − x Sc x O3 − x/2(OH) y : high-temperature 1H NMR studies

Abstract

The 1H nuclear magnetic resonance measurements were carried out to study proton dynamics features in the hydrated scandium-doped barium zirconate, BaZr1 − xScxO3 − x/2(OH)y, with x = 0.2 and 0.4 in the temperature range 300–600 K. The obtained data evidence a fast proton motion in both samples, which is characterized by the jump frequency of about 108 s−1 at 450 K. However, the microscopic nature of hydrogen diffusion in these two samples is quite different. For the sample with x = 0.2, hydrogen motion mechanisms are defined by a rapid chemical exchange between Sc–OH–Zr and Zr–OH–Zr positions. The estimated value of activation energy for hydrogen diffusion of about 0.5 eV is determined by the energy barrier produced by Sc3+ ion. The increase of Sc concentration to x = 0.4 leads to the drastic changes of sample properties. Experimental results allow to assume the formation of nanoscaled Sc-rich domains and the decomposition of hydrogen sublattice with formation of two proton subsystems: the protons in Zr–OH–Zr coordinations and those concentrated in Sc–OH–Sc environments. The proton motion in both these subsystems is rather fast, but the chemical exchange between them is highly suppressed. Hydrogen motion inside Sc-rich environments has most likely localized nature. Our estimates yield the energy values of about 0.25 and 0.55 eV for hydrogen motion in “free lattice” and in Sc-rich clusters, respectively. The Sc-rich domains can retain hydrogen up to 600 K.