Oxygen permeability of LaGa 0.65 Ni 0.20 Mg 0.15 O 3d ceramics: effect of synthesis method A.L. Shaula a , A.P. Viskup b , V.V. Kharton a,b,* , D.I. Logvinovich b , E.N. Naumovich b , J.R. Frade a , F.M.B. Marques a a Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, Aveiro 3810-193, Portugal b Institute of Physicochemical Problems, Belarus State University, 14 Leningradskaya Str., Minsk 220050, Belarus Received 13 September 2002; accepted 9 October 2002 Abstract Oxygen ionic transport in dense LaGa 0.65 Ni 0.20 Mg 0.15 O 3d membranes, prepared by the standard ceramic synthesis technique and via glycine-nitrate process (GNP), was studied using measurements of the total conductivity, oxygen permeation and faradaic ef®ciency (FE). At 1223 K oxygen transfer through LaGa 0.65 - Ni 0.20 Mg 0.15 O 3d ceramics is mainly determined by the bulk ambipolar conductivity, while decreasing temperature leads to a greater role of the surface exchange rate. In spite of moderate difference in the ceramic microstructures, the surface exchange limitations are considerably higher for the membranes prepared by the standard ceramic route compared to GNP-synthesized material. Thermal expansion and partial ionic and electronic conductivities were found essentially independent of the synthesis method. The level of oxygen ionic conduction in LaGa 0.65 Ni 0.20 Mg 0.15 O 3d , characterized by the activation energy of about 150 kJ/mol and ion transference numbers in the range 1  10 3 5  10 2 at 973±1223 K, is higher than that in La(Ga,Ni)O 3d perovskites and comparable to La 2 NiO 4 -based phases. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Oxides; Ceramics; Chemical synthesis; Ionic conductivity; Surface properties 1. Introduction Mixed-conducting ceramic membranes are of considerable interest for applications in electrocatalytic reactors for oxygen separation and conversion of light hydrocarbons to value-added products, particularly the conversion of natural to synthesis gas [1±7]. Conventional technologies for methane conversion are based on steam reforming and/or partial oxidation processes. Steam reforming is energy- intensive due to highly endothermic nature of the reaction, whereas the most signi®cant cost associated Materials Research Bulletin 38 (2003) 353±362 * Corresponding author. Tel.: 351-234-370263; fax: 351-234-425300. E-mail address: kharton@cv.ua.pt (V.V. Kharton). 0025-5408/02/$ ± see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII:S0025-5408(02)01024-3