High-Temperature Dielectric and Relaxation Behavior of Tantalum-Doped Sodium Bismuth Titanate-Barium Titanate Ceramics

Ta-doped 0.94Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3)[(1 - x)(0.94BNT-0.06BT) - xTa (x = 0.00-0.02)] ceramics were prepared by a solid-state reaction process. X-ray diffraction (XRD) shows a rhombohedral symmetry with space groupR3cfor all samples. The introduction of Ta moves the low-temperature dielectric anomaly to lower temperature while the high-temperature dielectric anomaly becomes broader, although the dielectric permittivity is depressed slightly. Dielectric permittivity (e(r)) as a function of temperature for the samplex = 0.02 shows a stable and broad relative permittivity similar to 3500 from 50 degrees C to 400 degrees C with low dielectric loss (tan delta) <= 0.02 from 80 degrees C to 340 degrees C (at 1 kHz). A Debye-like relaxation was found in the paraelectric region. The activation energy of relaxation frequency (E-a) of the samplesx = 0, 0.005, 0.01, 0.02 is 0.62 eV, 0.84 eV, 1.15 eV and 1.20 eV and the activation energy of conduction (E-con) is 0.56 eV, 0.72 eV, 0.89 eV and 0.90 eV forx = 0.00,x = 0.005,x = 0.01 andx = 0.02, respectively, which are derived from isothermal impedance spectroscopy and admittance spectroscopy, respectively. The dielectric relaxation behavior is related to the migration of oxygen vacancies and cation vacancies dependence on the concentration of Ta.