Protonic and electronic conductivity of the layered perovskite oxides HCa2Nb3O10 and Ca4Nb6O19

• Conductivity of layer perovskite HCa2Nb3O10 from 200 to 475 °C was re-investigated.
• In humidified H2, conductivity increases by four orders upon heating to 475 °C.
• Increase in conductivity is irreversible and much larger than that in humid air.
• The primary conduction mechanism is electronic under reducing conditions.

The structural and electrical properties of the Dion–Jacobson series layer perovskite HCa2Nb3O10 were investigated. Within the intermediate temperature range (200–475 °C), the compound undergoes topochemical dehydration to Ca4Nb6O19 and, under reducing atmospheres, partial reduction of Nb(V) to Nb(IV). These changes occur upon heating and are not reversed on cooling. Analysis of impedance data shows that the conductivity of Ca4Nb6O19 is predominantly electronic under reducing atmospheres, consistent with the behavior of other structurally related mixed-valence layered niobates.

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