Sr0.02La0.98Nb1-xTaxO4 (SLNT, with x = 0.1, 0.2, and 0.4) proton conducting oxides were synthesized by solid state reaction for application as electrolyte in solid oxide fuel cells operating below 600 degrees C. Dense pellets were obtained after sintering at 1600 degrees C for 5 h achieving a larger average grain size with increasing the tantalum content. Dilatometric measurements were used to obtain the SLNT expansion coefficient as a function of tantalum content (x), and it was found that the phase transition temperature increased with increasing the tantalum content, being T = 561, 634, and 802 degrees C for x = 0.1, 0.2, and 0.4, respectively. The electrical conductivity of SLNT was measured by electrochemical impedance spectroscopy as a function of temperature and tantalum concentration under wet (p(H2O) of about 0.03 atm) Ar atmosphere. At each temperature, the conductivity decreased with increasing the tantalum content, at 600 degrees C being 2.68 x 10(-4), 3.14 x 10(-5), and 5.41 x 10(-6) Scm(-1) for the x = 0.1, 0.2, and 0.4 compositions, respectively. SLNT with x = 0.2 shows a good compromise between proton conductivity and the requirement of avoiding detrimental phase transitions for application as a thin-film electrolyte below 600 degrees C. (C) 2011 Elsevier B.V. All rights reserved.