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) − x Ta ( x = 0.00–0.02)] ceramics were prepared by a solid-state reaction process. X-ray diffraction (XRD) shows a rhombohedral symmetry with space group R 3 c for 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 ( ɛ r ) as a function of temperature for the sample x = 0.02 shows a stable and broad relative permittivity ∼ 3500 from 50 °C to 400 °C with low dielectric loss (tan δ ) ≤ 0.02 from 80 °C to 340 °C (at 1 kHz). A Debye-like relaxation was found in the paraelectric region. The activation energy of relaxation frequency ( E a ) of the samples x = 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 for x = 0.00, x = 0.005, x = 0.01 and x = 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.