Diffuse phase transition and impedance spectroscopy analysis of Ba2.15−xNa0.7+xNb5−xWxO15 (x = 0.25) ferroelectric ceramic

A new rare earth ferroelectric tetragonal tungsten bronze compound with general formula Ba2.15−xNa0.7+xNb5−xWxO15 (x = 0.25) was elaborated as ceramic and investigated using X-ray diffraction and dielectric measurements. The results show a tetragonal phase with the space group P4bm. Special emphasis was done to characterize diffuse phase transition (DPT) that occurs close to 472 °C. Using dielectric measurements in a frequency range of (10 Hz–1 MHz) and in a temperature range (25–550 °C), we have shown that the real part of the permittivity close to DPT is well described by Santos–Eiras phenomenological model. Space charge polarization, relaxation phenomena and free charges conductivity have been analyzed using dielectric, impedance spectroscopy and Nyquist plots showed non-Debye (polydispersive) type relaxation. In paraelectric phase, the Arrhenius activation energies were determined. Frequency dependence of ac conductivity at different temperatures follows the Jonscher’s universal law (Jonscher et al. in J Mater Sci 20:4431, 1985).