Crystal structure, microstructure, electrical conductivity, and electrochemical performance of a family of iron perovskites with the general formula Ln(0.5)M(0.5)FeO(3-delta) (Ln = La and Pr; M = Sr, Ca, and Ba) has been studied as functions of mean A cation radius < r(A)>. All the samples have a rhombohedral structure (space group: R (3) over barc). Scanning electron microscope images show that the average grain size decreases with increasing < r(A)>. The dc four-probe measurements indicate that all samples have high electrical conductivity, increasing with < r(A)>. The electrochemical behavior of these cathode materials was evaluated by using current-voltage curve measurements and ac impedance spectroscopy over three-electrode electrolyte supported cells. The results show an improvement in cathode performance and a significant decrease in polarization resistance with increasing mean A cation radius < r(A)>. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3435321] All rights reserved.