In this work, the solid electrolyte Na3+xZr2-xMxSi2PO12, M = Ce4+, Gd3+ and Yb3+ compounds were synthesized by a solid state reaction. The ceramic samples were sintered in the temperature range 1150-1300 degrees C with 5 h holding time. X-ray diffraction, scanning electron microscopy (SEM) and complex impedance spectroscopy (IS) were used as experimental techniques. The investigated compounds at room temperature belong to monoclinic symmetry, and Ce4+, Gd3+ and Yb3+ ions substitution range decreases with increases of x, therefore, optimal concentration was fixed at x = 0.1. Results showed the significant influences of dopant ions and the processing condition on the microstructure and conductivity of these ceramics. Dense Ce4+ and Gd3+ doped samples were obtained at higher sintering temperature than Yb3+ doped and Na3Zr2Si2PO12 ceramics. A drop in grain boundary conductivity due to glassy phase formation in Na3Zr2Si2PO12 and Yb3+ doped compounds was observed. Maximum conductivity value at room temperature was obtained for Na3+xZr1.9Ce0.1Si2PO12 sample. (C) 2016 Elsevier Ltd. All rights reserved.