Ionic conduction in fluorite-type structure oxide ceramics Ce0.8M0.2O2-delta (M=La, Y, Gd, Sm) at temperature 400-800 degrees C was systematically studied under wet hydrogen/dry nitrogen atmosphere. On the sintered complex oxides as solid electrolyte, ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in the solid states proton conducting cell reactor by electrochemical methods, which directly evidenced the protonic conduction in those oxides at intermediate temperature. The rate of evolution of ammonia in Ce0.5M0.2O2-delta (M=La, Y, Gd, Sm) is up to 7.2 x 10(-9), 7.5 x 10(-9), 7.7 x 10(-9), 8.2 x 10(-9) mol s(-1) cm(-2), respectively. (c) 2005 Elsevier B.V. All rights reserved.