The present work reports the influence of Lanthanum (La) substitution on the structural, optical, electrical, and magnetic properties of bismuth ferrite (BiFeO3) nanoparticles (NPs). The compositions of Bi1−xLaxFeO3 (0% < x < 20%) NPs, with 5% Bi-excess, were synthesized through sol–gel conventional route. The XRD results suggest the formation of rhombohedral perovskite structure (R3c space group) along with a minor secondary phase. The crystallite size calculated from XRD and FESEM was observed to decrease from 60.0 to 40.0 nm with an increase in La content. The bandgap calculated using UV–Vis spectroscopy was found to decrease with La doping, and PL spectroscopy infers formation of defects in La–BFO NPs. The P–E loop studies reveal that La-doped BFO exhibits ferroelectric behavior at room temperature. The various parameters such as spontaneous polarization, dielectric constant, and distribution parameter of relaxation time measured from the electrical investigation were found to increase up to 5% La doping BFO then start decreasing with further increase in the La content in BFO. The impedance spectra of La–BFO was fitted using the theory of Cole–Cole with R(C(R(QR)))(CR) model. It is observed that La-concentration above 5% generates excess space charge which might cross the threshold to start conduction resulting in degrading of multiferroic properties. The DC magnetization study revealed the ferromagnetic behavior of the samples at room temperature. It is observed that La substitution affects the shape of the magnetization hysteresis curve beyond 5% La-concentration, and transforming it to a neck-like formation providing evidence for the spin-canting effect in the samples. These results make La-doped BiFeO3 NPs a propitious candidate for the multiferroic applications like high-density data storage devices and supercapacitors.

Role of La substitution on structural, optical, and multiferroic properties of BiFeO3 nanoparticles

The compounds Bi0.94Sm0.06FeO3, Bi0.92Sm0.06Y0.02FeO3, Bi0.90Sm0.06Y0.04FeO3, and Bi0.88Sm0.06Y0.06FeO3 were found to have the rhombohedral perovskite-like structure. The structural parameters were extracted from the X-ray diffraction data. The Fourier transform infrared spectroscopy revealed three absorption bands in the wavenumber range 400 – 2000 cm-1. The Bi0.94Sm0.06FeO3 and Bi0.92Sm0.06Y0.02FeO3 compounds were found to have similar weak ferromagnetic behaviors, whereas the ferromagnetism of the Bi0.88Sm0.06Y0.06FeO3 compound was found to be soft and substantially enhanced. The magnetic transition temperatures were in the range 340 – 350 °C.Physics

https://journalskuwait.org/kjs/index.php/KJS/article/download/7981/375

Enhanced magnetization in Y substituted Bi0.94Sm0.06FeO3 multiferroic ceramics

Polycrystalline Bi1−xBaxFeO3 (0 ≤ x ≤ 0.30) samples have been prepared by two stage solid state reaction method. The surface texture of the prepared material exhibited a uniform grain distribution with minor empty space suggesting that the density of the pelletized samples is high and grain size is found to decrease with Ba substitution. An important observation is the stabilization of a dielectric anomaly near the magnetic transition temperature in temperature dependent dielectric studies which is ascribed to the presence of magnetoelectric (ME) coupling. This ME coupling effect has been demonstrated by measuring the effect of varying magnetic fields on the dielectric constant. The dielectric constant increased with increasing applied magnetic field giving a coupling coefficient (er(H) − er(0))/er(0) of 1% at H = 5 kOe at room temperature which demonstrate the importance of these material from application point of view. The dielectric constant is high at low frequencies and is found to decrease at moderate frequencies indicating the Maxwell–Wagner contribution to the dielectric response. The increase in Ba content and temperature resulted in an increase in bulk resistance and exhibits a typical negative temperature coefficient of resistance behavior. A temperature dependent and non-Debye type of relaxation process is revealed by impedance spectroscopic studies. The conductivity spectra revealed the presence of hopping mechanism in the electrical transport process and the activation energies lying in the range from 0.45 to 0.70 eV indicate that the conduction of oxygen vacancies through hopping mechanism.

S. Adnan Raza

Papers

Investigation of dielectric and complex impedance spectroscopic studies of Bi 1−x Ba x FeO 3 (0 ≤ x ≤ 0.30) system