M. Sakar

Role of oxygen vacancy and Fe–O–Fe bond angle in compositional, magnetic, and dielectric relaxation on Eu-substituted BiFeO3 nanoparticles

The influence of oxygen vacancies on the dielectric relaxation behavior of pure and Eu-substituted BiFeO3 nanoparticles synthesized by a sol-gel technique has been studied using impedance spectroscopy in the temperature range of 90 °C to 180 °C. The electric relaxation time and activation energy of the oxygen vacancies can be calculated from the Arrhenius equation, and found to be 1.26 eV and 1.76 eV for pure and Eu-substituted BiFeO3, respectively. Substitution induces structural disorder and changes in the Fe-O-Fe bond angle, leading to alteration of the magnetic properties, observed from magnetic studies and evaluated using Rietveld refinement of the XRD patterns. X-ray photoelectron spectroscopy (XPS) confirms the shifting of the binding energy of the Bi 4f orbital, establishing Eu substitution at the Bi site. Calculation of the area under the Fe(2+)/Fe(3+) (2p) and O (1s) XPS spectra gives approximate values of the oxygen vacancies.

Large scale synthesis and formation mechanism of highly magnetic and stable iron nitride (ε-Fe3N) nanoparticles

e-Fe3N magnetic nanoparticles with an average size of 45 nm were synthesized by nitriding the zero valent iron nanoparticle precursors using ammonia gas as a reactive ambience. The technique reported in this study is found to be promising in producing highly stable e-Fe3N magnetic nanoparticles and can be extended to other forms of Fe-nitrides.

Manifestation of weak ferromagnetism and photocatalytic activity in bismuth ferrite nanoparticles

Bismuth ferrite (BFO) nanoparticles were synthesized by auto-ignition technique with and without adding ignition fuel such as citric acid. The presence of citric acid in the reaction mixture yielded highly-magnetic BFO/γ-Fe2O3 nanocomposite. When this composite was annealed to 650°C, a single phase BFO was formed with average crystallite size of 50 nm and showed weak ferromagnetic behavior. Conversely, the phase pure BFO prepared without adding citric acid exhibited antiferromagnetism because of its larger crystallite size of around 70 nm. The visible-light driven photocatalytic activity of both the pure BFO and BFO/γ-Fe2O3 nanocomposite were examined by degrading methyl orange dye. The pure BFO showed a moderate photocatalytic activity; while BFO/γ-Fe2O3 nanocomposite showed enhanced activity. This could be probably due to the optimal band gap ratio between BFO and γ-Fe2O3 phases reduced the recombination of electron-hole pairs which aided in the enhancement of photocatalytic activity.

Insights into the nitridation of zero-valent iron nanoparticles for the facile synthesis of iron nitride nanoparticles

The process of nitridation of zero-valent iron nanoparticles (ZVINPs) is investigated by employing two different synthesis strategies such as solvothermal method and gas diffusion using N2 and NH3. It is observed that the phase formation of different iron nitrides mainly depends on the reaction chemistry of the nitridation source and temperature. Accordingly, N2 gas diffusion and solvothermal methods yield iron oxide phases, whereas NH3 gas diffusion yields pure iron nitride phase with particle sizes in the nanoscale. X-ray diffraction studies complemented by Rietveld refinement confirm the formation of e-Fe3N and γ′-Fe4N nanoparticles. Field emission scanning electron microscopy images revealed spherical nanoparticles with average particle sizes of 35 and 50 nm for ZVINPs and iron nitride NPs, respectively. From the magnetization studies carried out using a superconducting quantum interference device magnetometer it is found that the field-dependent hysteresis curves indicated the ferromagnetic properties of ZVINPs, e-Fe3N and γ′-Fe4N NPs with coercive fields of 160, 65 and 45 Oe, respectively. Similarly, the temperature-dependent magnetization profiles revealed that the observed ferromagnetic properties of iron nitride phases can be attributed to the redistribution of electronic spin states due to both nitrogen populations and the confinement in the crystallites.

Evolution of silver/gold triangular nanoframes from prismatic silver/gold core/shell nanostructures and their SERS properties

We report the evolution of Ag/Au triangular nanoframes from nano core/shell of Ag/Au and their surface enhanced Raman scattering (SERS) properties. The Ag/Au prismatic core/shell nanostructures were synthesized using chemical reduction method. It was observed that, on the addition of excess gold chloride (HAuCl4) solution, the morphology of nano core/shell was changed to alloy like triangular nanoframes. Accordingly, a shift was found towards higher wavelengths in the UV-Visible absorption peaks of Ag/Au nanoframes compare to Ag/Au nano core/shell. Consequently, the SERS effect of these Ag/Au anisotropic nanostructures were studied on methylene blue. The Ag/Au alloy like prismatic nanoframes showed improved SERS effect than that of prismatic core/shell nanostructures. The experimental findings were revealed that the improved SERS effect could be resulted from the enhanced surface plasmon resonance (SPR) due to the alloy like construction of Ag/Au system.We report the evolution of Ag/Au triangular nanoframes from nano core/shell of Ag/Au and their surface enhanced Raman scattering (SERS) properties. The Ag/Au prismatic core/shell nanostructures were synthesized using chemical reduction method. It was observed that, on the addition of excess gold chloride (HAuCl4) solution, the morphology of nano core/shell was changed to alloy like triangular nanoframes. Accordingly, a shift was found towards higher wavelengths in the UV-Visible absorption peaks of Ag/Au nanoframes compare to Ag/Au nano core/shell. Consequently, the SERS effect of these Ag/Au anisotropic nanostructures were studied on methylene blue. The Ag/Au alloy like prismatic nanoframes showed improved SERS effect than that of prismatic core/shell nanostructures. The experimental findings were revealed that the improved SERS effect could be resulted from the enhanced surface plasmon resonance (SPR) due to the alloy like construction of Ag/Au system.

Optimization of processing temperature in the nitridation process for the synthesis of iron nitride nanoparticles

We have demonstrated an effective strategy on the nitridation process to synthesize e-Fe3N nanoparticles (NPs) from the zero valent iron NPs as a starting material. The transformation of iron into iron nitride phase was systematically studied by performing the nitridation process at different processing temperatures. The phase, crystal structure was analyzed by XRD. Morphology and size of the ZVINPs and e-Fe3N NPs were analyzed by field emission scanning electron microscope. Further, their room temperature magnetic properties were studied by using vibrating sample magnetometer and it revealed that the magnetic property of e-Fe3N is associated with ratio of Fe-N in the iron nitride system.

Effect of europium substitution on the magnetic and optical properties of nanostructured bismuth ferrite

Single phase Bi(1−x)EuxFeO3 multiferroic nanoparticles were synthesized by tartaric acid assisted sol-gel method and the effect of Eu substitution in Bismuth ferrite (BFO) was investigated on the structural, optical and magnetic properties. It was observed a gradual structural transition from rhombohedral R3c to orthorhombic Pbnm with the increase of Eu content resulted from the lattice distortion in BFO system due to the smaller radius of Eu3+ ions. The optical band gap of BFO was altered with respect to the change of particle sizes with the increment of Eu content. The magnetic property of Bi(1−x)EuxFeO3 system was found to be increased with the increase of Eu substitution. This might be attributed to the substitution-induced suppression of spiral spin modulation caused by an appropriate substitution of Eu in the BFO system.