Structure and Dielectric Behavior of Yb2O3-MgO Co-Doped 0.92BaTiO3-0.08(Na0.5Bi0.5)TiO3 Ferroelectric Relaxor

Dielectric properties and structure of 0.015Yb2O3-xMgO doped 0.92BaTiO3-0.08(Na0.5Bi0.5)TiO3 ceramics with x = 0.0–0.025 have been investigated. As Yb2O3-MgO was added into the BT-NBT, the phase changes from tetragonal to pseudo-cubic, with the tetragonality c/a decreases from 1.011 to 1.008 and XRD peaks broadened. The combined study of XRD and TEM image revealed a formation of core–shell structure in grains with core of 400–600 nm and the shell of a thickness 60–200 nm. There is a slowly phase transition against temperature from the variable temperature Raman analysis. The ferroelectric relaxor peak of BT-NBT decreases from ~4000 to ~2000 and a new broad dielectric peak with an equivalent maximum (εr′~2300) appears in the temperature dependent dielectric constant curve (εr′-T), which produces a flat εr′-T curve. Sample 0.92BaTiO3-0.08(Na0.5Bi0.5)TiO3-0.015Yb2O3-0.005 MgO and 0.92BaTiO3-0.08(Na0.5Bi0.5)TiO3-0.015Yb2O3-0.01MgO give a εr′ variation within ±14% and ±10% in 20–165 °C. The core–shell microstructure should take account for the flattened εr′–T behavior of these samples.