The barium ferrite BaTi_xFe_12-xO₁₉ (x = 0.2, 0.4, 0.6, 0.8) (BFTO-x) ceramics doped by Ti⁴⁺ were synthesized by a modified sol-gel method. The crystal structure and magnetic structure of the samples were determined by neutron diffraction, and confirm that the BFTO-x ceramics were high quality single phase with sheet microstructure. With x increasing from 0.2 to 0.8, the saturation magnetization (M_s) decreases gradually but the change trend of coercivity (H_c) is complex under the synergy of the changed grain size and the magnetic crystal anisotropy field. Relying on the high valence of Ti⁴⁺, double resonance peaks are obtained in the curves of the imaginary part of magnetic conductivity (μ′′) and the resonance peaks could move toward the low frequency with the increase of x, which facilitate the samples perform an excellent wideband modulation microwave absorption property. In the x = 0.2 sample, the maximum reflection loss (RL) can reach -44.9 dB at the thickness of only 1.8 mm, and the bandwidth could reach 5.28 GHz at 2 mm when RL is less than -10 dB. All the BFTO-x ceramics show excellent frequency modulation ability varying from 18 (x = 0.8) to 4 GHz (x = 0.4), which covers 81% of the investigated frequency in microwave absorption field. This work not only implements the tunable of electromagnetic parameters but also broadens the application of high-performance microwave absorption devices.

Multiferroic BiFeO₃-based ceramics were synthesized using the rapid liquid-phase sintering method. The rare-earth ion (Sm³⁺, Gd³⁺, Y³⁺) doping causes structural distortion without changing the intrinsic rhombohedral perovskite structure. Raman analysis shows that the effect of doping on E modes is greater than A₁ modes, and the microstructure of FeO₆ octahedron can be regulated by ion doping. A-site trivalent ion doped ceramics exhibit improved magnetism compared with pure BiFeO₃ ceramic, which originated from the suppressed spiral spin structure of Fe ions. The tilt of FeO₆ octahedron as a typical structure instability causes the anomalous change of the imaginary part of permittivity at high frequency, and doped ceramics exhibit natural resonance around 16-17 GHz.

Bismuth ferrite (BiFeO₃)-based materials are multiferroic materials widely studied. This study reports that strong ferroelectricity and enhanced magnetic performance are simultaneously obtained in the quenched (1-x)BiFeO₃-xBaTiO₃ (BFBT100x, x = 0.2 and 0.3) ceramics. Quenching treatment can reduce the amount of defects and Fe²⁺ ions and make the defect dipole in a random state, which is conducive to improving the ferroelectricity and magnetism. Compared with the conventional sintered samples, the quenched ceramics have higher remnant and saturation polarization. As for magnetism, the coercive field (H_c) of the quenched ceramics is smaller and the quenching treatment can increase the maximum magnetization by up to 15%.