Abstract:The Aurivillius layer-structures, described by the general formula Bi2O2(Am-1BmO3m+1), are naturally 2-dimensionally nanostructured. They are very flexible frameworks for a wide variety of applications, given that different types of cations can beaccommodated both at the A- and B-sites. In this review article, we describe how the Aurivillius phases are a particularly attractive class of oxides for the design of prospective single phase multiferroic systems for multi-state data storage applications, as they off… Show more
“…The three-layer structure of bismuth titanate (Bi 4 Ti 3 O 12 -BIT) has attracted researchers due to its high ferroelectric transition temperature (above 600 • C), low processing temperature compared to higher-layer structured compounds, and its anisotropic ferroelectric behavior [37][38][39][40][41]. However, these compounds possess high conductivity due to the volatile nature of bismuth at higher temperatures.…”
In the present work, we have synthesized rare-earth ion modified Bi4−xRExTi2Fe0.7Co0.3O12−δ (RE = Dy, Sm, La) multiferroic compounds by the conventional solid-state route. Analysis of X-ray diffraction by Rietveld refinement confirmed the formation of a polycrystalline orthorhombic phase. The morphological features revealed a non-uniform, randomly oriented, plate-like grain structure. The peaks evident in the Raman spectra closely corresponded to those of orthorhombic Aurivillius phases. Dielectric studies and impedance measurements were carried out. Asymmetric complex impedance spectra suggested the relaxation of charge carriers belonging to the non-Debye type and controlled by a thermally activated process. Temperature-dependent AC conductivity data showed a change of slope in the vicinity of the phase transition temperature of both magnetic and electrical coupling natures. Based on the universal law and its exponent nature, one can suppose that the conduction process is governed by a small polaron hopping mechanism but significant distortion of TiO6 octahedral. The doping of the A-sites with rare-earth element ions and changes in the concentrations of Fe and Co ions located on the B-sites manifested themselves in saturated magnetic hysteresis loops, indicating competitive interactions between ferroelectric and canted antiferromagnetic spins. The magnetic order in the samples is attributed to pair-wise interactions between adjacent Fe3+–O–Fe3+, Co2+/3+–O–Co3+/2+, and Co2+/3+–O–Fe3+ ions or Dzyaloshinskii–Moriya interactions among magnetic ions in the adjacent sub-lattices. As a result, enhanced magnetoelectric coefficients of 42.4 mV/cm-Oe, 30.3 mV/cm-Oe, and 21.6 mV/cm-Oe for Bi4−xDyxTi2Fe0.7Co0.3O12−δ (DBTFC), Bi4−xLaxTi2Fe0.7Co0.3O12−δ (LBTFC), and Bi4−xSmxTi2Fe0.7Co0.3O12−δ (SBTFC), respectively, have been obtained at lower magnetic fields (<3 kOe). The strong coupling of the Aurivillius compounds observed in this study is beneficial to future multiferroic applications.
“…The three-layer structure of bismuth titanate (Bi 4 Ti 3 O 12 -BIT) has attracted researchers due to its high ferroelectric transition temperature (above 600 • C), low processing temperature compared to higher-layer structured compounds, and its anisotropic ferroelectric behavior [37][38][39][40][41]. However, these compounds possess high conductivity due to the volatile nature of bismuth at higher temperatures.…”
In the present work, we have synthesized rare-earth ion modified Bi4−xRExTi2Fe0.7Co0.3O12−δ (RE = Dy, Sm, La) multiferroic compounds by the conventional solid-state route. Analysis of X-ray diffraction by Rietveld refinement confirmed the formation of a polycrystalline orthorhombic phase. The morphological features revealed a non-uniform, randomly oriented, plate-like grain structure. The peaks evident in the Raman spectra closely corresponded to those of orthorhombic Aurivillius phases. Dielectric studies and impedance measurements were carried out. Asymmetric complex impedance spectra suggested the relaxation of charge carriers belonging to the non-Debye type and controlled by a thermally activated process. Temperature-dependent AC conductivity data showed a change of slope in the vicinity of the phase transition temperature of both magnetic and electrical coupling natures. Based on the universal law and its exponent nature, one can suppose that the conduction process is governed by a small polaron hopping mechanism but significant distortion of TiO6 octahedral. The doping of the A-sites with rare-earth element ions and changes in the concentrations of Fe and Co ions located on the B-sites manifested themselves in saturated magnetic hysteresis loops, indicating competitive interactions between ferroelectric and canted antiferromagnetic spins. The magnetic order in the samples is attributed to pair-wise interactions between adjacent Fe3+–O–Fe3+, Co2+/3+–O–Co3+/2+, and Co2+/3+–O–Fe3+ ions or Dzyaloshinskii–Moriya interactions among magnetic ions in the adjacent sub-lattices. As a result, enhanced magnetoelectric coefficients of 42.4 mV/cm-Oe, 30.3 mV/cm-Oe, and 21.6 mV/cm-Oe for Bi4−xDyxTi2Fe0.7Co0.3O12−δ (DBTFC), Bi4−xLaxTi2Fe0.7Co0.3O12−δ (LBTFC), and Bi4−xSmxTi2Fe0.7Co0.3O12−δ (SBTFC), respectively, have been obtained at lower magnetic fields (<3 kOe). The strong coupling of the Aurivillius compounds observed in this study is beneficial to future multiferroic applications.
The citrate sol-gel process was used to produce Sr2FeO4 strontium ferrite powder. The method involves metallic nitrates, citric acid and distilled water as a solvent, followed by calcination. The Ruddlesden-Popper structure of the resulting compound was identified by XRD analysis. The different molecular structures and vibration bands were studied by FTIR. The morphology of the powder was analysed using SEM. Samples appear of good crystalline quality and with interesting nanostructure. We studied optical properties and determined the band gap energy to lie about 2.8 eV, Sr2FeO4 can thus absorb photons having a wavelength less than 444 nm, approximately, making this compound potentially interesting for applications.
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