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

Abstract

Infrared diffuse reflection spectra of O–H( ν OH) and O–D( ν OD) stretching vibration regions are used to characterize proton dissolution sites in high temperature proton conductors (HTPCs) of CaZrO 3, SrZrO 3 and BaZrO 3 doped with trivalent Ga 3+, In 3+ and Y 3+ ions. The number of observed ν OH band was three, five or six and two, respectively, for the CaZrO 3-, SrZrO 3- and BaZrO 3-based samples. It was inferred that the two lowest bands below 2000 cm −1 observed for SrZrO 3-based samples were the ν OH bands for hydrogen bonding of O…H. Therefore, the number of proton dissolution sites was concluded to be three for the CaZrO 3-based samples, three or four for the SrZrO 3-based samples and two for the BaZrO 3-based samples. The ν OH bands were observed at low wave numbers in the order of Sr(Zr,M III)O 3− δ <Ca(Zr,M III)O 3− δ <Ba(Zr,M III)O 3− δ , i.e., hydrogen bonding strength of the dissolved protons is found to be in the order of Ba(Zr,M III)O 3− δ <Ca(Zr,M III)O 3− δ <Sr(Zr,M III)O 3− δ . The average distances between two oxygen atoms, r O–O, in the original alkaline-earth zirconates are reported as r O–O(SrZrO 3)< r O–O(CaZrO 3)< r O–O(BaZrO 3). 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.