The conductivity and mean transport number of pyrochlore-type (La2-xCax)Zr2O7, where x was 0.15, 0.03 or 0.05, and La2(Zr2-xCax)O7, where x was 0.015, were studied as a function of temperature under wet H or O atmospheres. Under wet H atmospheres, pure proton conduction was observed below 873K for the (La2-xCax)Zr2O7 and La2(Zr2-xCax)O7 systems. The proton conductivities at 873K were equal to 6.8 x 10-2 and 1.0 x 10-2S/m for (La1.95Ca0.05)Zr2O7 and La2(Zr1.985Ca0.015)O7, respectively. The proton conductivity of (La1.97Ca0.03)Zr2O7 was some 3 times higher than that of La2(Zr1.985Ca0.015)O7, although the numbers of positive charges which were introduced by Ca2+ doping were equal for the 2 samples. The 3-times higher proton conductivity of (La1.97Ca0.03)Zr2O7 over that of La2(Zr1.985Ca0.015)O7 was attributed to the higher proton concentration in (La1.97Ca0.03)Zr2O7. This was suggested to be because the O, and/or vacant sites that were responsible  for  proton  dissolution,  were different  for  the  (La2-xCax)Zr2O7  and La2(Zr2-xCax)O7 systems. That is, the 8b and 48f O-sites for (La2-xCax)Zr2O7 and the 48f O-site for La2(Zr2-xCax)O7 may have contributed to proton dissolution. As a result, the proton conductivity of Ca2+-doped La2Zr2O7 depended upon both the Ca2+ doping level and the Ca2+ doping site. At temperatures above 873K, under a wet H atmosphere, the mean transport number of O ions increased with increasing temperature. Under a wet O atmosphere, positive holes were the dominant carriers in both systems; unlike the case for wet H atmospheres.

Electrical Properties of Proton Conducting Ca2+-Doped La2Zr2O7 with a Pyrochlore-Type Structure. T.Omata, S.Otsuka-Yao-Matsuo: Journal of the Electrochemical Society, 2001, 148[6], E252-61