Relaxation mechanisms in Sr0.3Ba0.7Nb2O6

Strontium barium niobate Sr0.3Ba0.7Nb2O6 exhibits a complex dielectric beha vior. Measurements performed over a wide frequency range (10(2)-10(9) Hz) a nd 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 epsilon(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 freque ncy range (10(8) 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 f requencies (Arrhenius-type behaviour) and comparison of the dielectric spec tra (Cole-Cole type relaxations).