Infrared study of high-temperature proton-conducting aliovalently doped SrZrO₃ and BaZrO₃ formation of YO₆ clusters in Y-doped SrZrO₃

Infrared spectra for the O-H stretching vibration, ν_OH, region were studied for Sc- and Y-doped SrZrO₃ and Y-doped BaZrO ₃ ceramics. For Sc-doped SrZrO₃ and Y-doped BaZrO ₃, two intense ν_OH bands at ∼ 3300 and ∼ 3030 cm^-1 were observed for the low doping level. With increasing doping level, two ν_OH bands at ∼ 2450 and ∼ 1900 cm^-1 appeared in addition to the bands at ∼ 3300 and ∼ 3030 cm^-1 and increased their intensities. However, intensities of the bands at ∼ 2450 and ∼ 1900 cm^-1 were considerably smaller than those of the bands at ∼ 3300 and ∼ 3030 cm^-1. In contrast to Sc-doped SrZrO₃, four bands at ∼ 3300, ∼ 3030, ∼ 2450, and ∼ 1900 cm^-1 were observed for the low doping level in Y-doped SrZrO₃; furthermore, the intensities of the four bands were comparable and independent of Y-doping level. Thus, the two bands at ∼ 3300 and ∼ 3030 cm^-1 were attributable to the proton bonded to the oxygen between dopant M^III and the host Zr ions, i.e., M ^III-OH-Zr. The bands at ∼ 2450 and ∼ 1900 cm^-1 were attributed to the proton bonded to the oxygen between the two dopants, i.e., M^III-OH-M^III The present results revealed that dopant Y in SrZrO₃ aggregated on an atomic scale and formed the YO₆ cluster even for the low doping level.