Infrared absorption spectra of high temperature proton conducting Ca2+-doped La2Zr2O7

Infrared (IR) absorption spectra of pyrochlore-type Ca2+-doped La2Zr2O7 pro ton conductors, i.e., (La2-xCax)Zr2O7-delta and La-2(Zr2-xCax)O7-delta syst ems, were studied by the diffuse reflection method. The O-H stretching vibr ations (v(OH)) due to the protons dissolved in the crystal with negligible effects of adhesion and/or adsorption water could be detected by improvemen t 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-xCax)Zr2O7-delta and the La-2(Zr2-xCax)O7-delta systems; t hree v(OH) bands at 3517, 3401, and 3323 cm(-1) for the (La2-xCax)Zr2O7-del ta system and six v(OH) bands at 3517, 3430, 3414, 3371, 3341, and 3289 cm 21 for the La-2(Zr2-xCax)O7-delta system were observed. The stable sites fo r 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 cond uctors. It was concluded that the O-H bonds in Ca2+-doped La-2 Zr2O7 crysta l are tight compared with perovskite-related-type proton conductors, and th at definite stable sites for protons exist in Ca2+-doped La2Zr2O7 crystal. In the IR spectra of (La2-xCax)Zr2O7-delta samples with various water vapor pressures, p(H2O), of proton dissolution treatment, the preferred dissolut ion of protons into the specific site was observed under low p(H2O) atmosph ere. The details of the dissolution environment of protons are also discuss ed. (C) 2001 The Electrochemical Society.