Characterization and dielectric properties of Sr4M2Ti4Ta6O30 (M = Pr and Eu) ceramics

Polycrystalline samples of Sr4Pr2Ti4Ta6O30 (SPIT) and Sr4Eu2Ti4Ta6O30 (SETT) were prepared by a high temperature solid-state reaction technique. The formation, structure, dielectric and ferroelectric properties of the compounds were studied. Sr4Eu2Ti4Ta6O30 is found to be a ferroelectric phase with filled tetragonal tungsten bronze (TB) structure at room temperature and undergoes a diffuse type ferroelectric-paraelectric phase transition around 90 degrees C with relaxor properties, while Sr4Pr2Ti4Ta6O30 belongs to paraelectric phase with TB structure at room temperature. At 1 MHz, SPIT exhibits a high dielectric constant of 181 and a low dielectric loss of 3.6 x 10(-3) with a negative temperature coefficient of the dielectric constant (tau(epsilon)), and SETT has a high dielectric constant of 192 and low dielectric loss of 7.7 x 10(-3) with a positive tau(epsilon) at room temperature, and heterogeneous mixtures of SPTT and SETT or a solid solution between them might be used to manufacture a tungsten bronze-structured temperature-stable dielectrics. (C) 2010 Elsevier B.V. All rights reserved.