RESUMO
The structural, magnetic and magnetoelectric properties were investigated for sol-gel prepared BaFe12O19 nanorods and plate-like nanoparticles. Based on comparative experiments with bulk ceramics, it is found that larger structural distortion is present in nanostructures, which could cause the enhancement of magnetocrystalline anisotropy and the off-center displacement of Fe3+ ions, and thus result in improved magnetic and magnetoelectric properties in BaFe12O19 plate-like nanoparticles. Meanwhile, the local (Fe2+-Fe3+) dipoles, which usually appear during a high temperature sintering process, can also contribute to the negative magnetoelectric effect of BaFe12O19 nanorods and a large room temperature magnetodielectric coefficient of about -13% is observed at 104 Hz and 9 kOe.
RESUMO
The relationship among dielectric anomaly, ferroelectric response, defects, and microstructures was established for (K0.48(1+x)Na0.52)0.95Li0.05Nb0.95Sb0.05O3 (x = 0.04, 0.00, -0.02, -0.04 and -0.08) ceramics. For x = -0.02 and -0.04, larger coercive fields and lower remnant polarizations were obtained; besides, an additional dielectric relaxation behavior was observed with the activation energy Ea being about 2.19 eV and 1.92 eV, respectively. Furthermore, the grain and grain boundary contributions to the capacitance were separated using impedance spectroscopy, which, combined with back-scattering characterization, firmly indicates the core-shell structure of K-deficient samples (x = -0.02 and -0.04). Unlike the cores, the shells possess a large amount of K+ vacancies (). This work paves a way for regulating the fine structure and more on the electrical properties of KNN-based materials.
