Quantum-mechanical calculations (Perdew-Becke-Ernzerhof version of density

functional theory) were carried out on 12.5%Y-doped BYZ periodic structures in

order to obtain energy barriers for intra-octahedral and inter-octahedral proton

transfers. Activation energy (Ea) values of 0.48 and 0.49eV were found for intraoctahedral

proton transfers on O–O edges (2.58 and 2.59Å) of ZrO6 and YO6

octahedra, respectively, and Ea = 0.41eV for the inter-octahedral proton transfer at

an O–O separation of 2.54Å. These results indicated that both the inter-octahedral

and intra-octahedral proton transfers were important in the BYZ electrolyte: the

calculated values bracketed the experimental value of Ea = 0.44eV. Based upon the

results obtained, an atomic-level proton diffusion mechanism and possible proton

diffusion pathways were proposed for the BYZ electrolyte. The thermal librations

of BO6 octahedra and uncorrelated thermal vibrations of the two oxygen atoms

participating in the hydrogen bond led to a chaotic fluctuation in the distances

between the O atoms involved in the hydrogen bonding. Such fluctuations affected the barriers and, at certain O–O separations, permitted the hydrogen atoms to move

within the hydrogen bonds from one potential minimum to the other and between

the hydrogen bonds. Synchronisation of these intra- and inter-H-bond motions

resulted in continuous proton diffusion pathways. Continuity of the proton

diffusion pathways was an essential condition required for fast proton transport.

Proton Diffusion Pathways and Rates in Y-Doped BaZrO3 Solid Oxide Electrolyte

from Quantum Mechanics. B.Merinov, W.Goddard: Journal of Chemical Physics,

2009, 130[19], 194707