Structural evolution and dielectric properties of (Ba1−xNdx)(Ti1−yFey)O3 ceramics

• Structural evolution and dielectric properties of (Ba1−xNdx)(Ti1−yFey)O3 were studied.
• A cubic ceramic with x = y = 0.05 exhibits a high-k Y5V behavior (εRT′ = 6790).
• The Tm in BNTF with x = 0.05 decreased linearly at a rate of −5 °C/mol% Fe ions.
• Evolution in the 840 cm−1 Raman band gives evidence for Nd3+–Fe3+ complex formation.
• Defect chemistry associated with structure evolution is discussed.

The influence of donor and acceptor co-doping on structure and dielectric properties of (Ba1−xNdx)(Ti1−yFey)O3 (BNTF) (x = 0.05, y = 0.01–0.07; and x = 0–0.08, y = 0.05) ceramics was investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), Raman spectroscopy, and dielectric measurements. When x < y, two types of Nd3+–Fe3+ and Fe3+–VO–Fe3+ defect complexes formed and could not coexist, leading to the mixed phases of cubic and hexagonal. A single-phase ceramic with a cubic or tetragonal structure formed for x ⩾ y and the dielectric-peak temperature (Tm) in BNTF with x = 0.05 decreased linearly with increasing y at a rate of −5 °C/mol% Fe ions. A high-k Y5V behavior can be realized at x = y = 0.05 (i.e., C-N5F5). The same concentrations of Nd3+ and Fe3+ formed Nd3+–Fe3+ complexes, which could effectively suppress the dielectric loss and silence the 840 cm−1 band called “Raman charge effect” associated with Nd3+ donors. C-N5F5 exhibited a cubic structure, medium-sized grains (3.3 μm), low dielectric loss (<0.06), and high-k Y5V behavior (εRT′ = 6790). Defect chemistry associated with structure evolution is discussed.