Short-range structure of proton-conducting perovskite BaInxZr1-xO3-x/2 (x=0-0.75)

In a systematic study, we investigate the effect of dopant level and hydration on the short-range structure of the proton-conducting perovskite-type oxide BaInxZr1-xO3-x/2 (x = 0 - 0.75), using infrared and Raman spectroscopy. The results show that the doping leads to significant local distortions of the average cubic structure of these materials. By increasing the In concentration from x = 0 to x = 0.75, new bands appear and grow in intensity in both the IR and the Raman spectra, showing that the local distortions become successively more and more pronounced. The structural distortions are largely uncorrelated to the presence of oxygen vacancies, but instead are mainly driven by the size and charge difference between the In3+ and Zr4+ ions, which leads to displacements of the cations and to tilting of the (In/Zr)O-6 octahedra. On the basis of our results, we suggest that there is a threshold between x = 0.10 and x = 0.25 where the structural distortions propagate throughout the whole perovskite structure. Comparison of our spectroscopic data with the proton conductivity for the same materials indicates that the presence of extended structural distortions is favorable for fast proton transport.