AC and DC electrochemical investigation of protonic conduction in calcium-doped barium cerate ceramics

Abstract

Protonic conduction in barium cerates doped with a divalent metal, BaCe, _1–xCa_xO_3–x(x= 0.02, 0.05, 0.10, 0.15), has been investigated at high temperature in a moist atmosphere. Conduction by protons was confirmed by emf measurements using specimen ceramics as the solid-electrolyte membrane separating moist and dry nitrogen atmospheres. Bulk electrical conductivity, σ_b measurements were carried out using impedance techniques. Plots of log(σ_bT)versus 1/T showed apparent Arrhenius behaviour. Conductivity increases markedly with increasing x for 0<x⩽0.05, but not forx0.10. The protonic conductivity for a 10% Ca-doped ceramic at 900 °C is ca. 2 × 10^–3 S cm^–1 with an ‘activation energy’ of 54 kJ mol^–1. At high temperature, dc measurements forx= 0.02 gave ‘conductivities’ approaching σ_b values obtained by impedance measurements, but contributions other than bulk resistance became increasingly significant at lower temperatures. Of those contributions, the electrode–electrolyte charge-transfer resistance was of particular importance.