Infrared Absorption Spectra of High Temperature Proton Conducting Ca²⁺-Doped La₂Zr₂O₇

Infrared (IR) absorption spectra of pyroehlore-type Ca²⁺-doped La₂r₂O₇ proton conductors, i.e., (La₂, Ca,)Zr₂O₇ .. δ and La2(Zr₂, Ca,)O₇ δ systems, were studied by the diffuse reflection method. The O-H stretching vibrations (v_OH) due to the protons dissolved in the crystal with negligible effects of adhesion and/or adsorption water could be detected by improvement of the Sample preparation and the diffuse reflection technique. The v_OH bands, due to protons dissolved in the crystal, were distinctly different between the (La₂, Ca,)Zr₂O₇ δ systems; three v_OH bands at 3517, 3401, and 3323 cm^-1 for the (La₂, Ca,)Zr₂O₇ δ system and six v_OH bands at 3517, 3430, 3414, 3371, 3341, and 3289 cm¹ for the La₂(Zr₂ Ca₂)O₇ - δ system were observed. The stable sites for dissolved protons were distinctly different between the two systems. The wave numbers and the widths of the v_OH bands were higher and much sharper than those reported for the well-known perovskite-related-type proton conductors. It was concluded that the O-H bonds in Ca²⁺-doped La₂Zr₂O₇ crystal are tight compared with perovskite-related-type proton conductors, and that definite stable sites for protons exist in Ca²⁺-doped La₂Zr₂O₇ crystal, In the 1R spectra of (La₂, Ca,)Zr₂O₇- δ samples with various water vapor pressures, PH₂O, of proton dissolution treatment, the preferred dissolution of protons into the specific site was observed under low PH₂O atmosphere. The details of the dissolution environment of protons are also discussed.