Ta2O5-doped 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 [(1 − x)(0.94BNT-0.06BT)-xTa (x = 0.00-0.02)] ceramics were prepared by a solid-state reaction technique. The single perovskite structure with space group R3c of the ceramics was identified by X-ray diffraction (XRD). Raman spectroscopy revealed the evolution of the local structure with Ta2O5 concentration. The temperature dependence of dielectric permittivity of the ceramics were deconvoluted by three Gaussian distribution functions which suggests that three dielectric anomalies exist in this system. The low-temperature dielectric anomaly exhibits a typical relaxor behavior with strong frequency dispersion (reentrant relaxor behavior). The activation energy derived from the V-F law is 0.298 eV, 0.338 eV, 0.412 eV and 0.449 eV, for x = 0.00, 0.005, 0.01 and 0.02, respectively. The mid-temperature and high-temperature anomalies are attributed to two structure phase transitions. The increase of the activation energies suggests that the coupling between polar clusters or polar nanoregions (PNRs) becomes weaker. The origin of the interaction between PNRs and phase transition behavior has been proposed according to the average structure, local structure and defect compensation mechanism of the system.

Ta-doped 0.94Bi 0.5 Na 0.5 TiO 3-0.06BaTiO 3 [(1 À x)(0.94BNT-0.06BT) À xTa (x = 0.00-0.02)] ceramics were prepared by a solid-state reaction process. Xray diffraction (XRD) shows a rhombohedral symmetry with space group R3c 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 (e 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 (tand) £ 0.02 from 80°C to 340°C (at 1 kHz). A Debyelike 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.

Sr(La1−xSmx)2Al2O7 (0 ≤ x ≤ 1) ceramics were synthesized by a standard solid-state reaction method, and the microwave dielectric characteristics were investigated together with the densification behavior, microstructure and phase composition.