Investigation of the rare earth-based LaYO3 (Y = Cr and Mn) perovskites by ab-initio approach

Innovative multi-layered Fe3O4-Gr/carbon/polypyrrole nanofiber composite: "a new frontier in dielectric enhancement and EMI shielding"

This study presents the synthesis and comprehensive characterization of an Fe3O4-Gr/carbon/polypyrrole nanofiber composite, highlighting its morphology as determined through Field Emission Scanning Electron Microscopy (FE-SEM) analysis, which reveals the small rod-like shape of the nano-fibers with an average diameter of 68 nm calculated from Image J software, contributing to a high surface area. X-ray diffraction (XRD) analysis confirms the effective formation of Fe3O4-Gr nanofibers, graphene, carbon, and polypyrrole (PPy), showcasing distinct crystallographic phases that strengthen the material's magnetic and conductive properties. The impedance plane plot indicates two relaxation processes at low and high-frequency regions from low to high-temperature ranges of 273 K to 363 K, reflecting complex electroactive charge transport dynamics within the nanofiber composite. Dielectric measurements demonstrate a high dielectric constant (up to 105) at lower frequencies, with a gradual decrease at higher frequencies, while tangent loss remains below 1 at higher frequencies and increases at lower frequencies with rising temperatures. The MVRH (Mott. Variable Range Hopping) model reveals a localization length of 1.5 Å, indicating localized charge carrier hopping, which contributes to the composite's electrical conductivity. The SPH (Small Polaronic Hopping) model suggests an activation energy of 1.43 eV, consistent with thermally activated charge carrier transport. In accordance with the double-well model, the conductivity plot also confirms the existence of dual relaxation peaks at low and high frequencies. Last but not least, the composite achieves 99.7% absorption and 99.8% attenuation across the x-band frequency range with a total shielding effectiveness (SET) of 28.4 dB at a thickness of 3 mm.

Structural, magnetic, electronic, optical and mechanical properties of actinide perovskite oxides XAnO3 [X = Cs+, Ba2+; An = Np5+, Np4+]: GGA, GGA+U and GGA+U+mBJ investigations

First-principles density functional theory (DFT)-based calculations were performed to investigate the structural, magnetic, electronic, optical and mechanical properties of two actinide perovskite oxides XAnO3, where [X = Cs+, Ba2+; An = Np5+, Np4+]. Wien2k software is utilized with GGA, GGA + U and GGA + U + mBJ potentials. The unit cell volumes for cubic (Pm-3m) structure of XAnO3 are optimized to achieve the ground state energy and equilibrium parameters. Substitution of X- and An-sites increases the lattice constant, a0 = 4.3998 Å (X = Cs+) and a0 = 4.4378 Å (X = Ba2+). The calculated band structure plus total and partial density of states using these methods confirm the 100 % spin-polarization and half-metallic (HM) nature of XAnO3 with Eg↓ = 2.731, 3.896 and 3.787 eV (X = Cs+); 3.891, 3.929 and 4.329 eV (X = Cs+). Total magnetic moment per unit cell of XAnO3 is respectively MTot = 2.0 and 3.0 μB revealing their ferromagnetic (FM) behavior with high Curie temperature (TC) within GGA, GGA + U and GGA + U + mBJ. Mechanical and thermodynamic stability of XAnO3 have been proved via the elastic parameters, sound velocity, Debye and melting temperatures, and enthalpy of formation. In addition, XAnO3 show amazing optical responses include high absorption, conductivity, refractivity, and reflectivity. These investigated properties confirm that XAnO3 materials have FM-HM and high optical characteristics and they perfectly suitable for many spintronics and optoelectronics applications such as sensors, storage devices and photodiodes.