Local structure of hydrated nanocrystalline films of the proton conductor BaZr1-xScxO3-x/2 studied by infrared spectroscopy

We report results from a study of the local structure of hydrated nanocrystalline 2 mu m films of the well known proton conductor BaZr1-xScxO3-x/2 with x = 0.45, 0.54 and 0.64, using infrared (IR) spectroscopy. The films were prepared by magnetron sputtering. Analysis of the IR spectra focused on the O-H stretching region (2000-3700 cm-1), which reveals the presence of several distinct O-H stretching bands for which the intensity and frequency of each band vary in an unsystematic manner with Sc concentration. The spectra for the two higher Sc concentrations, x = 0.54 and 0.64, exhibit a distinct, highly intense O-H stretching band centered at around 3400-3500 cm-1, which is assigned to relatively symmetric, weakly hydrogen-bonding, proton configu-rations. The spectrum for the lower Sc concentration, x = 0.45, does not feature such a band but a broader, weaker, O-H stretching band between approximately 2500 and 3700 cm-1, suggesting that the protons are more homogeneously distributed over a range of different local proton coordinations in this relatively weakly doped material. A comparison to the IR spectra of powder samples of similar compositions suggests that for x = 0.45, the spectra and proton coordination of films and powder samples are similar, whereas for x = 0.54 and 0.64, a larger fraction of protons seems to be located in weakly hydrogen-bonding proton configurations in the films compared to the respective powder samples.