Infrared study of high temperature proton conducting Sr(Zr0.95M0.05III)O3 − δ; formation of MIIIO6-cluster depends on dopant species

High temperature proton conductors of 5 at.% Ga-, Sc-, In-, Lu-, Y- and Gd-doped SrZrO3, i.e., Sr(Zr0.95MIII0.05)O3 − δ, were prepared and subjected to infrared analysis in the O–H stretching vibration, νOH, region using the diffuse reflection technique. The absorption intensities of the νOH bands at ∼ 3300 cm− 1 (band A) and ∼ 3030 cm− 1 (band B) due to MIII–OH–Zr and the bands at ∼ 2450 cm− 1 (band C) and ∼ 1900 cm− 1 (band D) due to MIII–OH–MIII were discussed in terms of the MIIIO6-cluster formation in Sr(Zr0.95MIII0.05)O3 − δ. The absorption intensity ratio of (IC + ID)/(IA + IB + IC + ID), which corresponds to the population of protons at the MIII–OH–MIII site to the total protons dissolved, increased since the ionic radius of the dopant MIII was different from that of the host Zr. It was shown experimentally that the structural distortion introduced by this MIII doping was the driving force for MIIIO6-cluster formation.