Structural, morphological and thermal analysis of pure and doped (Ho/Nd)-BFO multiferroics

Pure BiFeO3(BFO) and 20% doped BFO with Holmium (Ho) and Neodymium (Nd) separately (Ho-BFO and Nd-BFO) samples are synthesized using solid state reaction method. Structural characterization is carried out using XRD and FTIR analysis. Further morphological study is performed to assist the structural analysis. In addition to these, thermal analyses such as tg-DTA comparisons are also presented here. These studies provide the understanding of impact of doping in modifying structure and related inherent properties of BFO multiferroics which are normally associated with their tuned electric and magnetic properties.

Hydrogen Peroxide-Assisted Hydrothermal Synthesis of BiFeO3 Microspheres and Their Dielectric Behavior

Despite considerable efforts undertaken in a rapidly developing area of multiferroic research, synthesis of phase pure BiFeO3 is still a matter of intensive research. In this work, we report the shape-controlled synthesis of pure BiFeO3 microspheres via a facile hydrothermal route. The prepared BiFeO3 powder has been characterized using powder X-ray Diffraction (XRD), Differential Thermal analysis (DTA), Scanning Electron microscopy (SEM), and impedance spectroscopy. Powder XRD analysis confirms the formation of pure rhombohedrally distorted perovskite with R3c space group. Scanning electron micrograph revealed that the prepared BiFeO3 microspheres are nearly spherical in shape with uniform size distribution. The BiFeO3 microspheres exhibit a dielectric constant value of ~110 at 1000 KHz, which is higher than the BiFeO3 prepared by conventional solid-state reaction and sol–gel method. Variation of dielectric constant with temperature at different frequencies shows that the BiFeO3 has a dielectric anomaly of ferroelectric to paraelectric type at 1093 K and this phenomenon is well supported by TGA results.

Fabrication of Al2O3-coated BiFeO3 particles and fine-grained ceramics with improved electric properties

(1-x)BiFeO3@xAl2O3 ceramics with x = 0, 2.5, 5, and 7.5 mol% were prepared via the Stöber coating method. The effects of Al2O3 coating on microstructure, dielectric, and ferroelectric properties had been investigated. At x = 5 and 7.5, the samples had a great Al2O3 coating effect. XRD results indicated that excessive Al2O3 coating increased the formation of secondary phases (Bi2Fe4O9 and Bi24A12O39). After the coating of Al2O3, the samples had higher relative density and decreased loss tangent. Compared with the pure BiFeO3 sample, the Al2O3-coated samples had improved Bi-O strength, less oxygen vacancy, and the reduction of Fe3+ was decreased. The leakage current density decreased gradually. At x = 5, the sample had the highest Pr value (1.53 μC/cm2). These electric properties changes were ascribed to the generation of secondary phases, the fine grains, and the fewer vacancies.

Магнитные характеристики нанокомпозита на основе ферритов висмута

The magnetization processes of the BiFeO3 - Bi2Fe4O9 nanocomposite obtained by glycine nitrate combustion were studied. It was shown that the magnetic characteristics of the pure BiFeO3 and Bi2Fe4O9 compounds and the composite are significantly different. New properties of the synthesized substance are associated with the presence of exchange interaction at the interfaces.

Investigation of Polyol Process for the Synthesis of Highly Pure BiFeO3 Ovoid-Like Shape Nanostructured Powders

Exclusive and unprecedented interest was accorded in this paper to the synthesis of BiFeO3 nanopowders by the polyol process. The synthesis protocol was explored and adjusted to control the purity and the grain size of the final product. The optimum parameters were carefully established and an average crystallite size of about 40 nm was obtained. XRD and Mössbauer measurements proved the high purity of the synthesized nanostructurated powders and confirmed the persistence of the rhombohedral R3c symmetry. The first studies on the magnetic properties show a noticeable widening of the hysteresis loop despite the remaining cycloidal magnetic structure, promoting the enhancement of the ferromagnetic order and consequently the magnetoelectric coupling compared to micrometric size powders.

Synthesis, phase evolution and properties of phase-pure nanocrystalline BiFeO3 prepared by a starch-based combustion method

The preparation of phase-pure nano-sized BiFeO3 by a combustion-like methodusing starch as complexing agent is described herein. Phase evolution and development of thecrystallite size during the synthesis were monitored depending on the heat treatment and thecomposition of the (BiFe)-gels. Phase-pure BiFeO3 was obtained at a low heating rate andcalcination temperatures between 500 and 600 °C. Above 600 °C the BiFeO3 graduallydecomposed to Bi25FeO40 and Bi2Fe4O9. The investigations showed that the appearance ofsecondary phases depends on the heating rate, calcination temperature, and the fuel tooxidizer ratio in the (BiFe)-gel. The use of HNO3 instead of acetic acid in the preparation of the (BiFe)-gel promotes the formation of secondary phases. To study the phase stability thephase-pure BiFeO3 powder (1c) obtained after calcining at 550 °C (dcryst = 37 nm) wassintered to ceramic bodies up to 800 °C. During sintering the BiFeO3 phase decomposed toBi25FeO40 and Bi2Fe4O9 gradually. The activation energy for the decomposition processduring sintering was calculated to 337±19 kJ/mol using the (JMAK) model. Magnetic measurements on phase-pure BiFeO3 powders showmaximal magnetization of about 0.7 emu/g at 90 kOe and coercivities between 5−7 kOe at300 K. Investigations at 10 K reveal a loop shift (exchange-bias) up to 2.9 kOe in the negativedirection. The optical band gaps of the phase-pure BiFeO3 powders were determined as2.28(4) eV.