Preparation of pure and Sm-doped Na0.5Bi0.5TiO3 nanosized powders by sol-gel method and their electrical properties

摘要

The sol-gel method was applied to synthesize Na0.5Bi0.5TiO3 (NBT) sols and ceramic powders by using glycol as solvent and the optimized condition was determined. The optimized preparation parameters were selected as follows: reaction temperature = 20 A degrees C, pH of sol system = 3.5, n(NBT):n(glycol) (mol) = 1:12, drying temperature = 150 A degrees C, annealing temperature = 350 A degrees C and calcination temperature = 700 A degrees C. In this condition, the prepared powders show pure perovskite phase and good crystalline structure with uniform size about 50 nm, and their resistivity was 3.71 x 10(6) Omega m at room temperature. Then, Sm-doped Na0.5Bi0.5TiO3 ceramic powders were also prepared by using the sol-gel method, and the changes in constitution, structure, and electrical properties before and after Sm-doping were characterized. The resistivity of modified NBT powders was distinctly decreased after Sm-doping. With an increase in Sm content, the resistivity first increases and then decreases, and its lowest value was 2.41 x 10(5) Omega m with 0.5 at% Sm content. The dielectric properties of modified NBT powders were also improved by Sm-doping, which reveals a higher dielectric constant, stable dielectric constant curve and dielectric loss curve with an increase in frequency. XRD and SEM analyses demonstrate that there are no new phases appearing in Sm-doped specimens, but the cell parameters have changed and grain size has increased, which would be devoted to the enhancement of the electrical properties.