Hoang, T. P., Truong-Son, L. V., Phan, Lien, Nghiem, N. T., Truong-Tho, N., Tiep, N. H., Jabarov, S. H., Tien, D. P. T., Tran, T. A., Dang, N. T., Bich, D. D., and Khan, D. T.
The co-substitution effect of La and Fe ions on structural characterization, ferroelectric and magnetic properties, and energy storage efficiency of multiferroics Ba1-xLaxTi1-xFexO3 (0 ≤ x ≤ 0.20) was systematically studied utilizing a combination of x-ray diffraction, scanning electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), ferroelectric, and magnetic measurements. The results show a structural transformation from the P4mm tetragonal phase to the Pm-3m cubic one at x = 0.04, with no hexagonal phase across the entire large doping range, which differs from the results previously reported for BaTiO3 systems doped solely with Fe. The XPS results show single valence states of Ba, La, and Ti ions, alongside a mixed valence state of Fe in the investigated samples. Magnetic measurements indicate that the pristine sample (x = 0) exhibits weak ferromagnetic (FM) phases within a diamagnetic (DM) matrix. At x < 0.10, the FM and DM phases are suppressed while the paramagnetic phase becomes dominant, indicating no interaction between Fe ions and a reduction in lattice intrinsic defects such as O and Ti vacancies. For 0.10 ≤ x ≤ 0.15, Fe ions start to couple with each other, enhancing the ferromagnetism. However, as x = 0.20, the saturation magnetization is significantly reduced, indicating competition between FM and antiferromagnetic interactions between Fe ions. Ferroelectric measurements demonstrate the ferroelectric nature of the lightly doped samples (x ≤ 0.10) and the lossy improper ferroelectric nature of the samples with 0.15 ≤ x ≤ 0.20. The lossy improper ferroelectricity is related to electron hopping between the Fe3+–Fe4+ interaction pathways. The coercive electric field, remnant polarization, and maximum polarization decrease with the increase of the porosity in the samples. Furthermore, Ba1-xLaxTi1-xFexO3 exhibits high energy storage efficiencies of up to ~ 77%. These findings demonstrate an effective way to make efficient energy storage materials through optimizing doping level and morphological properties in BaTiO3 and other ferroelectrics. [ABSTRACT FROM AUTHOR]