Structure and conductivity of acceptor doped La2BaZnO5 and Nd2BaZnO5

• Conductivity of unusual structure-type containing ZnO4 tetrahedra investigated
• Calcium substitution introduces oxygen vacancies and enhances conductivity.
• Total oxide ion conductivity of up to 2 × 10− 3 S cm− 1 in La1.85Ca0.15BaZnO5 − δ
• Significant p-type contribution found in oxidizing conditions
• Protonic defects influence the total conductivity at intermediate temperatures.

The effect of calcium substitution on the structure and electrical conductivity of Ln2 − xCaxBaZnO5 − δ, Ln = La and Nd, has been studied. Differing trends with respect to dependence of the unit cell volume were observed as a function of Ca substitution. For both series of materials the limit of Ca substitution was estimated to be x ≈ 0.2. The electrical conductivity was studied in the temperature range of 1000–350 °C using electrochemical impedance spectroscopy in argon and oxygen atmospheres and via isotherms between 400 and 1000 °C as function of oxygen pressure and the water vapour pressure. A marked increase in conductivity of approx. two orders of magnitude was explained by the presence of oxygen vacancies in the calcium doped samples. At pO2 < 10− 12 atm the x = 0.15 materials are predominantly oxygen ion conductors, and La1.85Ca0.15BaZnO5 − δ displays a peak conductivity of 0.002 S cm− 1 at 1000 °C. The materials display a rise in conductivity in oxidizing conditions, indicating a significant p-type contribution.