Structure and dielectric properties of sodium-doped Ba(FeNb)0.5O3

The lower valence compensation of the Ba1−xNax(Fe0.5Nb0.5)1+x/4O3 (x = 0, 0.01, 0.05, 0.10, and 0.20) system was synthesized using a solid-state reaction, and the characteristics, including phase formation, microstructure and dielectric properties, were also investigated. XRD results indicate that the structure of BFN is cubic and transforms to orthorhombic when the Na+ ion concentration is ≧10 mol%. The SEM results indicate that the grain size of Ba1−xNax(Fe0.5Nb0.5)1+x/4O3 samples increase from x = 0.0 to 0.05, but decrease from 0.1 to 0.2 which is caused by the formation of acceptors N a B a 2 + + ′ at the grain boundaries that inhibits grain growth. Large and small grains coexist for Ba(FeNb)0.5O3 doped with 5 mol% Na+ ions. The step-like dielectric relaxor curve obtained for the doping concentration is 10 mol%. The dielectric constant and loss of Ba1−xNax(Fe0.5Nb0.5)1.025O3 ceramics are increased from 2 × 104–105 to 6 × 104–1.3 × 105 and 0.4–1.6 to 0.25 when x is increased from 0.1 to 0.2, respectively. Complex impedance spectroscopy indicated that the orientation and space charge polarization are dominant for the barrier layers Ba1−xNax(Fe0.5Nb0.5)1+x/4O3 dielectric behavior.