A novel GdSmZr2O7-(Li0.52Na0.48)(2)CO3 composite electrolyte material is successfully developed by pressureless-sintering for intermediate temperature solid oxide fuel cells. GdSmZr2O7 nanopowders are synthesized by a low cost chemical coprecipitation and calcination method. The phase structure and morphology as a function of the calcination temperature are investigated by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The resulting GdSmZr2O7 nanopowders after calcination at 800 degrees C for 5 h exhibit good crystallization and uniform particle morphology with an average size of 50 nm. The GdSmZr2O7-40 wt.% (Li0.52Na0.48)(2)CO3 composite sintered at 600 degrees C for 1 h has a high conductivity of 0.54 S cm(-1) at a temperature of 600 degrees C. From the Arrhenius curve of the composite, the activation energy has different temperature behaviors around the knee region of 480 degrees C, where the slope changes and separates the intrinsic oxygen vacancy conduction dominated region from the 'superionic highway' region. For GdSmZr2O7-40 wt.% (Li0.52Na0.48)(2)CO3 composite at temperatures above 480 degrees C, there is good correlation between ionic diffusivity and conductivity. The introduction of (Li0.52Na0.48)(2)CO3 carbonate into GdSmZr2O7 ceramics significantly promotes the enhancement of its conductivity by one or two orders of magnitude at the intermediate temperatures, especially above 480 degrees C. A maximum power density of 221 mW cm(-2) at 650 degrees C was achieved for excellent performance of fuel cell based on GSZ-40LN composite electrolyte. (C) 2018 Elsevier Ltd. All rights reserved.