Effect of acceptor dopants on the proton mobility in BaZrO3:: A density functional investigation

In this work, the stability and mobility of protonic defects in acceptor doped BaZrO3 are investigated using density functional theory in conjunction with kinetic modeling. The interaction between the mobile protons and Zr-site substituted trivalent dopants-Ga, Sc, In, Y, and Gd-is assessed by extensive mapping of migration pathways. In all cases, the interaction is attractive, which results in a stabilization, and hence a reduction of the mobility, of the proton. However, its strength and range vary substantially and are found to be strongly correlated to the ionic radius of the dopant. Further, it is shown that the observed correlation is related to a variation in strength of hydrogen bonds formed between protons and next nearest lattice oxygen ions in different environments. Finally, migration barriers and attempt frequencies obtained from first principles are used as input to a jump-diffusion model. The proton self-diffusion coefficient is evaluated for the different substituted phases, and the experimental trend in activation energies is reproduced.