Mechanical and impedance spectroscopy studies on the fast oxide ion conductor Na0.54Bi0.5Ti0.94Mg0.06O2.94

The perovskite structure Na0.5Bi0.5Ti0.94Mg0.06O2.94 sample was prepared by the conventional solid state reaction. The electrical properties and the mechanism of oxide ion diffusion in the Na0.5Bi0.5Ti0.94Mg0.06O2.94 compounds were investigated with the method of AC impedance spectroscopy and internal friction spectroscopy. The bulk oxide ionic conductivity of the Na0.5Bi0.5Ti0.94Mg0.06O2.94 compound at 673 K is about 3.3 x 10(-4) S/cm, 1.2 times higher than that of the Na0.5Bi0.5TiO3 sample at the same temperature. A prominent relaxation internal friction peak was observed and the relaxation parameters is E = 0.92 eV, tau(0) = 1.6 x 10(-13) s. Compared with the Na0.5Bi0.5TiO3 compound, the factors of the higher oxygen vacancy content and better oxygen vacancy mobility are responsible for the oxide ionic conductivity improvement of the Na0.5Bi0.5Ti0.94Mg0.06O2.94 sample. By the investigation of dielectric frequency spectroscopy in the temperature range from 473 to about 720 K, the Arrhenius plot of the Na0.5Bi0.5Ti0.94Mg0.06O2.94 sample was divided into two parts by an inflection point ( 540 K), which corresponds to the transition between the rhombohedral anti-ferroelectric phases to the tetragonal para-electric phase in the Na0.5Bi0.5Ti0.94Mg0.06O2.94 sample. The activation energies of oxide ionic diffusion in the rhombohedral and tetragonal structure Na0.5Bi0.5Ti0.94Mg0.06O2.94 sample are about 0.94 and 0.62 eV, respectively. The oxygen vacancy mobility of the tetragonal structure Na0.5Bi0.5Ti0.94Mg0.06O2.94 sample is superior to that of the rhombohedral structure Na0.5Bi0.5Ti0.94Mg0.06O2.94 sample, which is meaningful to improve the oxide ionic conductivity of the Na0.5Bi0.5TiO3-based materials.