Lead-Free Aurivillius Phase Bi2LaNb1.5Mn0.5O9: Structure, Ferroelectric, Magnetic, and Magnetodielectric Effects

Effective Enhancement of the Ferroelectric Performance of Polar Co-Gallate MOF by Doping M2+ Ions (M = Mg, Mn, Ni) into Framework Nodes

MOF ferroelectrics have been demonstrated to be a promising candidate owing to various structures and controllable properties. However, weak ferroelectricity hampers their boom. Herein, a convenient strategy, doping metal ions into the framework nodes of parent MOF, is adopted to enhance ferroelectric performance. A series of M-doped Co-Gallate (M = Mg, Mn, Ni) were synthesized to improve ferroelectric properties. The electrical hysteresis loop demonstrated its ferroelectric behaviors, exhibiting obviously improved ferroelectric properties compared with the parent Co-Gallate. The remanent polarization was enhanced by two times for Mg-doped Co-Gallate, six times for Mn-doped Co-Gallate, and four times for Ni-doped Co-Gallate. The promoted ferroelectric performances are ascribed to the enhanced polarity of the overall structure triggered by framework distortion. Intriguingly, ferroelectric behaviors increase in the order Mg < Ni < Mn, displaying the same tendency as the difference value in the ionic radius between Co²⁺ ions and M²⁺ metal ions (M = Mg, Mn, Ni). These results demonstrate doping of metal ions is a valid strategy to enhance ferroelectric performances, which may serve as a guide in modulating ferroelectric behaviors.

Relationship between the Synthesis Method and the Magnetoelectric Properties of Bismuth Sodium-Potassium Titanate/Nickel Cobalt Ferrite Lead-Free Composites

In this work, the influence of the synthesis methods of piezoelectric and magnetostrictive phases on the final properties of the Bi_0.5(Na_0.8K_0.2)_0.5TiO₃-Ni_0.5Co_0.5Fe₂O₄ composites was studied. Different routes were used to individually synthesize each phase, and the composites were prepared using different fractions for each phase. Composites were sintered, and the structural, microstructural, dielectric, and magnetoelectric properties were evaluated. According to the selected synthesis method employed for each phase, different particle sizes and reactivities of the individual phases were obtained. These differences determined the suitable sintering temperature for each set of composites and were responsible for the final properties. In fact, magnetoelectric properties were modulated by the combination of composition and synthesis routes.

Influence of the Addition of Rare Earth Elements on the Energy Storage and Optical Properties of Bi0.5Na0.5TiO3-0.06BaTiO3 Polycrystalline Thin Films

Rare earth element-doped Bi_0.5Na_0.5TiO₃-BaTiO₃ (BNT-BT-RE) polycrystalline thin films were processed on a platinized substrate by chemical solution deposition. The microstructure, dielectric, and ferroelectric properties were investigated for all prepared films. It was found that the incorporation of rare earth elements into the BNT-BT matrix increases both the dielectric constant and the breakdown strength while maintaining low dielectric losses, leading to an enhancement of the energy storage density to W_rec = 12 and 16 J/cm³ under an effective field of E = 2500 kV/cm, for Nd- and Dy-based films, respectively. The optical properties of films containing the lanthanide element were investigated and the obtained results bear interest for luminescence applications. The simultaneous appearance of ferroelectric and optical properties in the system under investigation is very promising for advanced optoelectronic devices.

Magnetodielectric Properties of Ordered Microstructured Polydimethylsiloxane-Based Magnetorheological Elastomer with Fe3O4@rGO Nanoparticles

Magnetodielectric properties of prepared ordered microstructured polydimethylsiloxane-based magnetorheological elastomer with the Fe₃O₄@rGO (Fe₃O₄@rGO/PDMS-MRE) were investigated to expand the application of magnetorheological elastomer (MRE) in magnetic sensing fields by improving the magnetodielectric effect. Five types of Fe₃O₄@rGO electromagnetic biphasic composite particles were synthesized by the solvothermal method, and their characterization and magnetic properties were also tested. Microstructurally ordered Fe₃O₄@rGO/PDMS-MRE samples with different Fe₃O₄@rGO concentrations were obtained through the magnetic field orientation technique, an experimental platform for magnetodielectric properties was built, and the relative permittivity of the samples was tested under magnetic flux density from 0 to 500 mT. The results show when the ratio of modified Fe₃O₄ to GO reaches 10:1, the Fe₃O₄@rGO composite particles exhibit uniform distribution with a flaky structure and strong magnetic properties and have the best bonding effect of composite particles. The relative permittivity of Fe₃O₄@rGO/PDMS-MRE increases with the rise of Fe₃O₄@rGO concentration and applied magnetic flux density. The relative permittivity of Fe₃O₄@rGO/PDMS-MRE with Fe₃O₄@rGO concentration of 60 wt% reaches 12.934 under the action of 500 mT magnetic flux density, and the magnetodielectric effect is as high as 92.4%. A reasonable mechanism for improving the magnetodielectric effect of ordered microstructured Fe₃O₄@rGO/PDMS-MRE is proposed.

Solid State Processing of BCZT Piezoceramics Using Ultra Low Synthesis and Sintering Temperatures

Lead-free (Ba_0.92Ca_0.08) (Ti_0.95 Zr_0.05) O₃ (BCZT) ceramics were prepared by a solid-state route (SSR) using ultra-low synthesis (700 °C/30 min and 700 °C/2 h) and sintering temperatures (from 1150 °C to 1280 °C), due to prior activation and homogenization by attrition milling of the starting high purity raw materials for 6 h before the synthesis and of the calcined powders for 3 h before the sintering. The comparison of the thermal analysis of the mixture of the starting raw materials and the same mixture after 6 h attrition milling allowed to evidence the mechanisms of activation, resulting in a significant decrease of the perovskite formation temperature (from 854 °C down to 582 °C). The secondary phases that limit the functional properties of the ceramic and their evolution with the sintering conditions were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), which allowed the design of a two-step sintering method to eliminate them. A pure tetragonal BCZT perovskite phase (P4mm, c/a = 1.004) and homogeneous ceramic microstructure was obtained for synthesis at 700 °C for 2 h and sintering with the use of a two-step sintering treatment (900 °C for 3 h and 1280 °C for 6 h). The best electromechanical properties achieved were d₃₃ = 455 pC/N, k_p = 35%, Q_m = 155.