The dielectric and optical properties of Fe1-xCoxNbO4 (x = 0 and 0.10) ceramics were investigated by impedance spectroscopy, electric modulus analysis, and diffuse reflectance measurements. The electrical response reveals thermally activated relaxation processes associated with grain and grain-boundary contributions, dominated by hopping conduction mediated by oxygen vacancies and localized mixed-valence states. Activation energies in the range of 0.52-0.74 eV were obtained from Arrhenius analysis. Cobalt substitution leads to higher impedance values and an enhanced dielectric constant, indicating modifications in lattice structure and defect distribution. Optical measurements exhibit strong UV-visible absorption for both compositions, while Co incorporation reduces the absorption intensity and slightly decreases the optical band gap, evidencing changes in the electronic structure and metal-oxygen interactions. These results highlight the role of Co substitution in tuning the dielectric and optical properties of FeNbO4-based ceramics.
Bi1−xNdxFeO3 (x = 0.01, 0.03,0.05, and 0.07) nanoparticles have been synthesized by ethylene glycol-based sol-gel technique. Through X-ray diffraction (XRD)technique, the phase purity was confirmed and it was also found that the rhombohedral distorted perovskite structure remain unaltered. The average sizes determined from the XRD peak broadening decreased from 40.7 nm for pristine BFO NPs to 37.5 nm for 7
The dielectric and optical properties of Fe1−xCoxNbO4 (x = 0 and 0.10) ceramics were investigated by impedance spectroscopy, electric modulus analysis, and diffuse reflectance measurements. The electrical response reveals thermally activated relaxation processes associated with grain and grain-boundary contributions, dominated by hopping conduction mediated by oxygen vacancies and localized mixed-valence states. Activation energies in the range of 0.52–0.74 eV were obtained from Arrhenius analysis. Cobalt substitution leads to higher impedance values and an enhanced dielectric constant, indicating modifications in lattice structure and defect distribution. Optical measurements exhibit strong UV-visible absorption for both compositions, while Co incorporation reduces the absorption intensity and slightly decreases the optical band gap, evidencing changes in the electronic structure and metal–oxygen interactions. These results highlight the role of Co substitution in tuning the dielectric and optical properties of FeNbO4-based ceramics.
This study presents the synthesis and electrochemical evaluation of a MIL-101(Cr)/V₂CTₓ@MgH₂ ternary heterostructure for hybrid energy-storage applications. The composite was designed by integrating porous MIL-101(Cr), conductive V₂CTₓ MXene, and redox-active MgH₂ to combine ion-accessible porosity, rapid electron transport, and faradaic charge-storage contribution within one electrode architecture. In a three-electrode configuration, the MIL-101(Cr)/V₂CTₓ@MgH₂ electrode delivered a specific charge capacity of 1290 C g⁻¹, exceeding the performance of the individual components. An asymmetric MIL-101(Cr)/V₂CTₓ@MgH₂//AC supercapattery device was further assembled using the ternary composite and activated carbon. The device achieved a specific charge capacity of 440 C g⁻¹ and delivered an energy density of 86.4 Wh kg⁻¹ at a power density of 1600 W kg⁻¹, while retaining 83.6
This study systematically investigates the influence of configurational entropy on the phase structure, microstructure, defect chemistry, and dielectric properties of four A-site disordered perovskite ceramics (Ba, La)TiO3, (Ba, La, Sr)TiO3, (Ba, La, Sr, Ca)TiO3, and (Ba, La, Sr, Ca, Bi)TiO3. X-ray diffraction analysis indicates that all compositions exhibit a single perovskite structure. With increasing configurational entropy, the diffraction peaks systematically shift to higher angles. Rietveld refinement confirms a reduction in unit cell volume, providing direct evidence of lattice contraction. Scanning electron microscopy suggests that the high-entropy sample exhibits a smaller average grain size compared to the low-entropy counterpart. This reduction is attributed to the hysteresis diffusion effect and suppressed grain boundary migration arising from lattice distortion. X-ray photoelectron spectroscopy analysis shows that high-entropy conditions promote the partial reduction of Ti4+ to Ti3+ and the increased concentration of oxygen vacancies, forming defect dipoles through the charge compensation mechanism. Dielectric measurements reveal that the (Ba, La, Sr, Ca, Bi)TiO3 composition exhibits a dielectric constant of 3.06 × 105 at 100 Hz, twice that of (Ba, La)TiO3, and a dielectric loss as low as 0.004 in the high-frequency regime. Impedance spectroscopy verifies that the internal barrier layer capacitance mechanism dominates the dielectric response, with an activation energy of 0.52–0.63 eV corresponding to thermally activated migration of oxygen vacancies. We demonstrate that configurational entropy engineering achieves an optimized balance between high dielectric constant and low dielectric loss by synergistically regulating lattice strain, microstructure, and defect chemistry, providing a new strategy for advanced dielectric materials.
