O-H stretching vibrations of proton conducting alkaline-earth zirconates

Infrared diffuse reflection spectra of OH(v(OH)) and O-D(v(OD)) stretching vibration regions are used to characterize proton dissolution sites in high temperature proton conductors (HTPCs) of CaZrO3, SrZrO3 and BaZrO3 doped with trivalent Ga3+, In3+ and Y3+ ions. The number of observed v(OH) band was three, five or six and two, respectively, for the CaZrO3-, SrZrO3- and BaZrO3-based samples. It was inferred that the two lowest bands below 2000 cm(-1) observed for SrZrO3-based samples were the v(OH) bands for hydrogen bonding of O...H. Therefore, the number of proton dissolution sites was concluded to be three for the CaZrO3-based samples, three or four for the SrZrO3-bascd samples and two for the BaZrO3-based samples. The v(OH) bands were observed at low wave numbers in the order of Sr(Zr,M-III)O3-delta < Ca(Zr,M-III)O3-delta < Ba(Zr,M-III)O3-delta, i.e., hydrogen bonding strength of the dissolved protons is found to be in the order of Ba(Zr,M-III)O3-delta < Ca(Zr,M-III)O3-delta < Sr(Zr,M-III)O3-delta. The average distances between two oxygen atoms, r(O-O), in the original alkaline-earth zirconates are reported as r(O-O)(SrZrO3)<r(O-O)(CaZrO3)<r(O-O)(BaZrO3). Strong hydrogen bonding was observed for the alkaline earth zirconate with short r(O-O). It was concluded that the chemical environment of protons dissolved was primarily affected by crystal structure of the original zirconates. (C) 2004 Elsevier B.V. All rights reserved.