Pure perovskite Pb[(Mg1/3Nb2/3)(0.8)(SC1/2Nb1/2)(0.2)]O-3 (PMNSN) ceramics were prepared via a modified 'columbite-type' method. The 1:1 B-site ordered structure was detected by X-ray diffraction and transmission electron microscopy. The dielectric relaxation behavior was described by a Lorentz relation and a small polaron over the Curie temperature range. The dielectric tunability properties were investigated at 300 K and 10 kHz. A high dielectric tunability (similar to 75% at 30 kV/cm), low dielectric loss (similar to 0.003) and high figure of merit (similar to 250) of PMNSN, indicate that PMNSN is a promising dielectric tunable material. The high dielectric non-linear behavior of PMNSN was further discussed in terms of the Landau-Ginsberg-Devonshire thermodynamic theory completed with a Langevin term that describes the contribution of the re-orientation of the polar nanoclusters to the non-linear epsilon(E) dependences. (c) 2012 Elsevier Ltd. All rights reserved.