High temperature proton conductors of 5 at.% Ga-, Sc-, In-, Lu-, Y- and Gd-cloped SrZrO3, i.e., Sr(Zr0.95M0.05III)O3 - delta, were prepared and subjected to infrared analysis in the 0-H stretching vibration, volt, region using the diffuse reflection technique. The absorption intensities ofthe v(OH) bands at similar to 3300 cm(-1) (band A) and similar to 3030 cm(-1) (band B) due to M-III-OH-Zr and the bands at similar to 2450 cm(-1) (band C) and similar to 1900 cm(-1) 11 (band D) due to M-III-OH-M-III were discussed in terms of the (MO6)-O-III-cluster formation in Sr(Zr0.95M0.05III)O3 - delta. The absorption intensity ratio of (I-C+I-D)/(I-A+I-B+I-C+I-D), which corresponds to the population of protons at the M-III-OH-M-III site to the total protons dissolved, increased since the ionic radius of the dopant M-III was different from that of the host Zr. It was shown experimentally that the structural distortion introduced by this M-III. doping was the driving force for (MO6)-O-III-cluster formation. (c) 2005 Elsevier B.V. All rights reserved.