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.

Non-ambient X-ray and neutron diffraction of novel relaxor ferroelectric xBi2(Zn2/3,Nb1/3)O3–(1 – x)BaTiO3

The first determination of the phase diagram of the novel ferroelectric relaxor xBi(Zn2/3Nb1/3)O3–(1 − x)BaTiO3 (BZN-BT) has been achieved with a combination of high-resolution X-ray and neutron diffraction up to the miscibility limit near x(BZN) = 20.0% over a temperature range 20 < T < 400 K. The combined X-ray and neutron data show that the instability within the xBZN-(1−x)BT system reaches a maximum at x = 3.9% and is driven by B-site displacement and distortion of the oxygen octahedra in the polar phases. Composition-dependent effects include a narrow Amm2-dominated region focused at x = 3.9%, significant convergence of the lattice parameters in both P4mm and Amm2 phases, and sharp maxima in piezoelectric coefficient d 33 and maximum polarization P max. Lattice parameter dilation at x ≥ 4.0% was observed for both P4mm and Amm2 unit cells, alongside the first appearance of Pm 3 m at 295 K and the onset of significant dielectric relaxation. Low-temperature neutron diffraction indicated a weak or non-existent temperature dependence on the transition from ferroelectric at x = 3.9% to ferroelectric relaxor at x = 4.0%. Temperature-dependent phase transitions were eliminated near x = 3.0%, with the ferroelectric limit observed at x = 5.0% and a transition to a low-loss relaxor dielectric near x = 8.0%.

Bismuth zinc niobate: BZN-BT, a new lead-free BaTiO3-based ferroelectric relaxor?

The novel lead-free ferroelectric relaxor system [Formula: see text](Bi([Formula: see text] [Formula: see text][Formula: see text](1[Formula: see text]BaTiO3 ([Formula: see text]BZN(1[Formula: see text]BT) has received interest as a high-capacity relaxor dielectric material. Small quantities (< 10.0 mol.%) of BZN-based dopant had significant impacts on the structure of the BaTiO3 host. This study evaluates the effect of BZN additions to the BaTiO3 host up to [Formula: see text]BZN = 10.0%. Initial additions of BZN were observed to stabilize tetragonal and orthorhombic coexistence at 295 K, alongside increasing dielectric constant. Peak dielectric constant and polarization were observed at [Formula: see text] < 4.0%, coinciding with maximum orthorhombic intensity and a local minima in tetragonal intensity. Compositions 0 < [Formula: see text] < 4.0% showed increasing polarization and a drop in [Formula: see text] and classical ferroelectric properties. No significant dielectric dispersion was observed for compositions [Formula: see text] < 4.0% over the frequency range 5–640 kHz. Compositions at [Formula: see text] > 4.0% showed the onset of dielectric relaxation alongside a drop in polarization coincident with a drop in the tetragonal [Formula: see text]/[Formula: see text] ratio and the onset of the cubic phase at 295 K. Peak piezoelectric, dielectric and polarization values occurred over the range 3.8% < [Formula: see text] < 4.0%, alongside maximum orthorhombic intensity. Subsequent BZN additions showed a rapid onset of dielectric relaxation, alongside an increase in cubic intensity and a continuous drop in [Formula: see text] with a minima near [Formula: see text] = 7.0%. Tetragonal presence at 295 K also vanished to zero at [Formula: see text] = 7.0%. Polarization loops ceased showing ferroelectric characteristics at [Formula: see text] > 5.0%, showing a transition from lossy relaxor dielectric to low-loss relaxor dielectric at [Formula: see text] > 10.0%.