Proton diffusion pathways and rates in Y-doped BaZrO3 solid oxideelectrolyte from quantum mechanics

摘要

We carried out quantum mechanical calculations (Perdew-Becke-Ernzerhof flavor of densityfunctional theory) on 12.5 Y-doped BaZrO3 (BYZ) periodic structures to obtain energy barriers forintraoctahedral and interoctahedral proton transfers. We find activation energy (Ea) values of 0.48and 0.49 eV for the intraoctahedral proton transfers on O–O edges (2.58 and 2.59 ) of ZrO6 andYO6 octahedra, respectively, and Ea=0.41 eV for the interoctahedral proton transfer at O–Oseparation of 2.54 . These results indicate that both the interoctahedral and intraoctahedral protontransfers are important in the BYZ electrolyte. Indeed, the calculated values bracket theexperimental value of Ea=0.44 eV. Based on the results obtained, the atomic level proton diffusionmechanism and possible proton diffusion pathways have been proposed for the BYZ electrolyte.The thermal librations of BO6 octahedra and uncorrelated thermal vibrations of the two oxygenatoms participating in the hydrogen bond lead to a somewhat chaotic fluctuation in the distancesbetween the O atoms involved in the hydrogen bonding. Such fluctuations affect the barriers and atcertain O–O distances allow the hydrogen atoms to move within the hydrogen bonds from onepotential minimum to the other and between the hydrogen bonds. Concertation of these intra- andinter-H-bond motions results in continuous proton diffusion pathways. Continuity of protondiffusion pathways is an essential condition for fast proton transport.