Abstract
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.
Highlights
There are many researches focused on the improvement of the εr 0 -T curve by the additions of some oxides into BaTiO3, such as Nb2 O5, MgO, Co3 O4, MnCO3 [4], and many BT-based ferroelectric relaxors reported
For c/a ≈ 1, it is hard to recognize between tetragonal and cubic ones, which are considered as a pseudo-cubic phase
The phase of the BT-NBT system transforms from transforms from tetragonal to pseudo-cubic with the “average” tetragonality c/a ≈ 1.008 tetragonal to pseudo-cubic with the “average” tetragonality c/a ≈ 1.008 (Figure 1c)
Summary
In multi-layer ceramic capacitors (MLCC), ideal materials should give a high εr 0 and a flat εr 0 -T curve (relaxed) in the operation temperature range. There are many researches focused on the improvement of the εr 0 -T curve by the additions of some oxides into BaTiO3 , such as Nb2 O5 , MgO, Co3 O4 , MnCO3 [4], and many BT-based ferroelectric relaxors reported. MgO shows the significant effects to the dielectric behavior and microstructure of BT ceramics [5,6,7]. A suitable MgO-Nb2 O5 -Na0.5 Bi0.5 TiO3 -BT relaxor ceramic can achieves an EIA-X9R standard, showing ∆C/C20◦ C = −1.8, 1.8, and −5.69% at. (Na0.5 Bi0.5 )TiO3 (NBT for short) with a perovskite structure is one of the most important ferroelectric material, which shows a high Curie temperature Tc ~ 593 K. We prepared Yb2 O3 MgO doped BT-NBT ceramic samples and investigated the XRD, Raman, and dielectric behaviors
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