Dielectric and structural properties of diffuse ferroelectric phase transition in Pb_1.85K_1.15Li_0.15Nb₅O₁₅ ceramic

¹ LMCN, F.S.T.G. University Cadi Ayyad Marrakech, Marrakech, Morocco
² LPMC, Université de Picardie, 33 rue Saint-Leu, 80039 Amiens Cedex, France
³ LPMC, Équipe Physique de l'environnement, Université Chouaib DoukKali, F.S. El Jadida, Morocco
⁴ University of Nîmes, Department of Sciences, Rue du Dr Georges Salan, 30021 Nîmes Cedex 01, France and C2M, Institut C. Gerhardt, UMR-CNRS 5253, 34095 Montpellier Cedex 05, France
⁵ Dipartimento di Fisica, Universita di Roma II “Tor Vergata”, Via della Ricerca Scientifica, 00133 Roma, Italy

Corresponding author: mezdaoud@yahoo.fr

Received: 12 February 2010
Revised: 28 September 2010
Accepted: 22 November 2010
Published online: 28 January 2011

Abstract

We studied the structural and dielectric properties of new Tetragonal Tungsten Bronze (TTB) ceramics Pb_1.85K_1.15Li_0.15Nb₅O₁₅ 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 E_τ = 0.72 eV. We demonstrated that frequency dependence of ac conductivity at different temperatures obeys the Jonscher's universal law: σ_ac = σ_dc + A(ω)ⁿ.