Abstract

Strontium barium niobate Sr_0.3Ba_0.7Nb₂O₆ exhibits a complex dielectric behavior. Measurements performed over a wide frequency range (10²–10⁹ Hz) and as a function of temperature have allowed a complete description of the relaxation mechanisms observed. At low frequency and below the temperature of the maximum of ε′_r (T_m = 303 K), a relaxor behavior is detected and correlated to the cationic disorder in pentagonal and tetragonal sites of the tungsten bronze structure. Moreover a network relaxation is clearly observed at high temperature in the paraelectric phase in the radio frequency range (10⁸ Hz). By analogy with perovskites, it can be related to the motion of Nb⁵⁺ ions in octahedral sites. The two relaxation mechanisms are described through both thermal evolution of the corresponding relaxation frequencies (Arrhenius-type behaviour) and comparison of the dielectric spectra (Cole–Cole type relaxations).