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NiO-BaTiO 3 composites were prepared by sintering BaTiO 3 together with NiO in air at 1300°C. Microstructure and morphology of the composites were detected by XRD and SEM, and the dielectric properties were measured by LCZ meter. The results indicate that the perovskite phase is formed in fact in status of solid solution doped with Ni 2+ , although only a small amount of Ni ions can dissolve into the perovskite phase. Ni doping decreases the formation temperature of the composite without inhibiting the grain growth of the crystalline phase. The dielectric constant decreases sharply and the dielectric loss decreases smoothly with increasing Ni 2+ below NiO addition of 0.5 wt.%. When NiO addition increases above 0.5 wt.%, the dielectric constant and loss correlate with mixing rule of the two phases. Meanwhile, the replacement of Ni 2+ for Ti 4+ decreases the Curie temperature of perovskite phase by 30°C.

In recent years, Schiff base-related conjugated systems have received extensive attention, but little research has been done in the field of electromagnetic materials. In this work, an organic conjugated system based on polypyrrole/hydrazone Schiff base (PPy/HSB) composites was constructed via a Schiff base synthetic route and their electromagnetic behavior was investigated. The electromagnetic response of PPy/HSB complexes demonstrates fine electromagnetic absorption performance. When the filler loading is 30 wt% in a paraffin matrix, an absorption peak of −43.1 dB was achieved and its effective absorption bandwidth (EAB) was located in the range of 10.88−18.0 GHz. The electromagnetic response behavior of PPy/HSB complexes is explained by models involving electronic structure, multi-polarization and conductive network. The mechanisms of PPy/HSB complexes formation and HSB crystallization are also discussed through the compatibility of PPy/HSB and the structure of HSB. Moreover, the morphology transformation of HSB in the PPy/HSB systems has been studied. This study opens the exploration of organic–dielectric conjugated systems in the field of electromagnetic materials, and significantly broadens the application range of organic–dielectric–dielectric composites.

The moderation of the dielectric properties of polymer composites and their environmental stability need to be considered comprehensively in the design of microwave-absorbing materials. In this work, polypyrrole/polystyrene (PPy/PS) composited particles were synthesized through a facile in situ bulk polymerization procedure. The PS component can be modulated conveniently by controlling the polymerization time. FTIR and Raman analyses disclosed that the PS component was immobilized in PPy via covalent bonds. The electromagnetic characterization results indicated that the dielectric properties and, thus, the microwave absorption could be controlled when the styrene polymerization was prolonged from 6 h (PPy-6) to 19 h (PPy-19). The composite PPy-19 displayed an optimal reflection loss of −51.7 dB with a matching thickness of 3.16 mm, and the effective absorption bandwidth (EAB) even reached 5.8 GHz at 2.4 mm. The PS component endowed PPy/PS composites with more robust environmental stability than homogeneous PPy. After being exposed to air for 365 days and hydrothermally treated at 100 °C for 12 h, PPy-19 still exhibited a reflection loss superior to −20 dB. The present work provides a new insight into the adjustment of the electromagnetic properties of PPy composites to fabricate high-performance microwave absorbers with superior environmental stability.

Endowing composites with defects such as oxygen vacancies is an easy and effective strategy to determine the physical and chemical properties of nanomaterials. The influence of defects on microwave absorption remains a very open question. Herein, MnO2/Ti3C2T x MXene composites are self-assembled, demonstrating the boosting of microwave absorption through Ni doping in MnO2 to modulate the oxygen vacancies. The Ni-doped MnO2 (Ni–MnO2) nanorods with diameters of about 40 nm are dispersed on the surface and interlay of MXene. As expected, the reflection loss (RL) value and effective absorption bandwidth (EAB) of Ni–MnO2/MXene composites are −55.9 dB and 6.32 GHz, which are greatly enhanced over pure MnO2/MXene with −18.8 dB and 4.56 GHz. This excellent microwave absorption is mainly attributed to the optimized impedance matching in Ni–MnO2/MXene composites. In addition, the random distribution of MnO2 nanorods and MXene layers will form a conductive network, leading to the inducing microcurrent to form conduction losses. Moreover, interfacial polarization between layered MXene and Ni–MnO2 and dipole polarization induced by oxygen defects yield a strongly dielectric loss. Thus, our work provides a novel principle of modulation in oxygen vacancies to develop efficient MXene-based multicomponent composites for electromagnetic wave absorption.

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