R. A. M. Gotardo

Ferroic states and phase coexistence in BiFeO3-BaTiO3 solid solutions

In this paper structural, electric, magnetic, and Mossbauer spectroscopy studies were conducted in (x)BiFeO3–(1-x)BaTiO3, 0.9 ≥ x ≥ 0.3, solid solutions. X-ray diffraction and Rietveld refinement studies indicated the formation of single-phased materials crystallized in a distorted perovskite structure with the coexistence of rhombohedral and monoclinic symmetries. Room temperature ferroelectric hysteresis loops showed that the electric polarization increases with the increase of the BaTiO3 content due to the singular structural evolution of the studied solid solutions. All samples presented weak ferromagnetic ordering, which indicates that the BaTiO3 substitution in the BiFeO3 matrix released the latent magnetization. Mossbauer studies revealed a magnetic spectral signature corresponding to ordered Fe3+ ions, and a decrease of the magnetic hyperfine magnetic fields with the increase of the BaTiO3 content. The composition 0.3BiFeO3–0.7BaTiO3 presented a spectral signature corresponding to a paramagnetic b...

Ferroic investigations in LuFe2O4 multiferroic ceramics

In this paper, the ferroic properties of polycrystalline LuFe2O4 samples were carefully investigated, and a dissimilar charge ordered state was identified. Strong dielectric dispersion, between 350 K and 225 K; the formation of cluster glass magnetic phases in the same temperature range; and the existence of a ferrimagnetic transition at 230 K indicate the coupling between the ferroelectric and the magnetic orders. Mossbauer spectroscopic investigations, at room temperature, revealed unbalanced contributions of the ferric and ferrous iron ions to the charge ordered state.

Structural Refinement and Ferroic Properties in BiFeO3–Based Compounds

Nanostructured BiFeO3 - XTiO3 (X = Ba or Pb) multiferroic ceramics were processed by mechanosynthesis and a detailed structural study was conducted through Rietveld refinement of X-ray diffraction patterns. It was found that the structural and ferroic properties have been improved by the formation of double-phased compounds in both cases. In fact, ferroelectric investigations indicated a structurally tuned ferroic state, where the ferroelectricity is strongly affected by the coexistence of two distinct symmetries in BiFeO3 -based solid solutions.