We studied the structural and dielectric properties of new Tetragonal
Tungsten Bronze (TTB) ceramics
Pb1.85K1.15Li0.15Nb5O15 that was synthesized by
solid-state reaction. We pay a special attention to the diffuse phase
transition (DPT) that occurs close to 425 °C. Using dielectric
measurements in a frequency range of 10 Hz–1 MHz and in the temperature range
30–560 °C, we have shown that the real 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 spectroscopy impedance and modulus
characterization. Cole-Cole plots show a non-Debye (polydispersive) type
relaxation. In paraelectric phase the Arrhenius activation energy was
determined as Eτ = 0.72 eV. We demonstrated that frequency
dependence of ac conductivity at different temperatures obeys the
Jonscher's universal law: σac = σdc + A(ω)n.