The effect of calcium substitution on the structure and electrical conductivity of Ln(2 - x)Ca(x)BaZnO(5 - delta), 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 approximate to 0.2. The electrical conductivity was studied in the temperature range of 1000-350 degrees C using electrochemical impedance spectroscopy in argon and oxygen atmospheres and via isotherms between 400 and 1000 degrees 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 pO(2) < 10(-12) atm atm the x = 0.15 materials are predominantly oxygen ion conductors, and La1.85Ca0.15BaZnO5 - delta displays a peak conductivity of 0.002 S cm(-1) at 1000 degrees C. The materials display a rise in conductivity in oxidizing conditions, indicating a significant p-type contribution. (C) 2015 Elsevier B.V. All rights reserved.