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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]

The pressure-driven phase transformation in polycrystalline BaTi 1 − x FexO3 (x = 1 %), synthesized by a solid-state reaction method, was investigated using synchrotron X-ray diffraction and Raman spectroscopy. All measurements were performed at room temperature within a large pressure range up to 36.5 GPa. The results clearly demonstrate a phase transformation from the ferroelectric tetragonal structure of P4mm symmetry to the paraelectric cubic structure of Pm-3m symmetry in the studied sample at the pressure of about 18 GPa. This phase transformation pressure is much higher than those previously reported for BaTiO3-based systems, indicating the stabilization of the ferroelectric phase by doping 1% Fe into BaTiO3. Feature modes of the tetragonal phase still persist while some new modes appear in the Raman spectra at pressures above 18 GPa. This is probably due to accumulated stress and/or local microscopic disorders in the sample, which are associated with the displacement of the Ti atoms along unit-cell diagonals. [ABSTRACT FROM AUTHOR]

We have investigated the hydrogen-annealing influence on the crystalline and electronic structures, and magnetic properties of La2/3Ca1/3MnO3 (LCMO). The results have indicated that the annealing at 700 and 900°C (labeled as LCMO-700 and LCMO-900, respectively) readily reduced single-phase LCMO, resulting in a complex phase composition of several isostructural oxygen-deficient perovskite-type phases coexisting with the Ruddlesden-Popper (La/Ca)2MnO4-type phase. While a Mn3+/Mn4+ mixed valence is present in LCMO, the hydrogenannealed samples mainly have Mn2+ and Mn3+ ions. Under such circumstance, large changes in magnetic parameters have been recorded, such as remarkable decreases in values of the magnetization, the Curie temperature (from 251 K for the as-prepared LCMO through 240 K for LCMO700 to ³221 K for LCMO-900), and the magnetic-entropy change. Particularly, the crystal and electronic-structure changes also enhance the magnetic inhomogeneity, resulting in a strong development of the Griffiths phase, and cause the first-to-second-order phase transformation. These results reflect the instability of the LCMO perovskite-type manganite versus hydrogenation. [ABSTRACT FROM AUTHOR]