Guohao Dai,Ruixiang Deng,Tao Zhang,Yun Yu,Lixin Song
High-entropy oxides (HEO) with high stability and designability are potential microwave absorbers that serve in harsh environments. However, loss design is critical for the absorption performance of HEO due to its weak intrinsic loss capability. Inadequate loss ability results in considerable secondary reflection. Here, an in situ conductive heterogeneous phase is constructed in (Fe 0.2x Co 0.2 Ni 0.2 Cr 0.2 Mn 0.2 ) 3 O 4 ( x = 1–5) using a reductive circumstance, to form a dual-phase composite. Both the ohmic and dielectric loss are enhanced as the conductive phase is introduced, while great impedance matching condition is well maintained. Hence, the composites can achieve substantial absorption across the whole X or Ku band with a thin thickness. Furthermore, key efforts are made to reveal the relationship between the absorbing performance and loss capability of an absorber. The analytical expression of the theoretical threshold of attenuation constant is derived. Based on the statistics of experimental data, the broad feasibility and practicability of the proposed theoretical threshold of attenuation constant are confirmed and discussed. Combined with both the theoretical and experimental studies, the mechanism by which the conductive phase contributes to increased absorption is also disclosed, providing an effective basis for the loss design of broadband microwave absorbers.
Wenchao Xue,Hua Li,Roberto Dugnani,Hafeez Ur Rehman,Chunmei Zhang,Yujie Chen,Hezhou Liu
In this study, a lead zirconate titanate (PZT)/in situ polymerized polyurethane (PU) composite with three-dimensional (3D) reduced graphene oxide (rGO) as the conductive phase was prepared and the potential of 3D rGO to enhance the damping properties was investigated. The conductivity and damping properties of the composite were systematically investigated. The results show that the conductive threshold of the composite is reached at a very low rGO content of about 0.7 wt% by using the 3D rGO structure. The best damping performance of the piezoelectric damping composite is achieved at the conductive threshold, where the loss factor is 0.22 (almost 41%) higher and the temperature range where tan δ ≥ 0.3 is 13.2 °C (almost 84%) wider than those of the PU matrix. A composite consisting of only PU and rGO sheets without the 3D structure was prepared for comparison. The conductive threshold of this composite is more than 0.9 wt% and the highest tensile strength is 5.63 MPa when the rGO content is 0.6 wt%, indicating that the 3D structure reduces the use of the conductive phase and does not significantly affect the tensile strength of the matrix.
Flexible magnetic field sensors are essential for small dimensions, excellent precision, and flexibility in narrow gap or pipe environments. A spiral conductive polymer composite has been proposed for magnetic field detection. To investigate how conductive phase content impacts its magnetic sensitivity, the relationship between magnetic flux density and voltage difference/magnetic sensitivity was examined with different carbon nanotube contents (1 wt%∼20 wt%). From the perspectives of the equivalent network and magnetic susceptibility, the voltage difference /magnetic sensitivity of the composite was analysed by varying its carbon nanotube content. The addition of carbon nanotubes creates a contradiction in the magnetic sensitivity caused by internal equivalent impedance or induced current. The experiments demonstrate that the interpolar voltage difference /magnetic sensitivity first increases and then sharply decreases with increasing carbon nanotube content within composites. The optimum carbon nanotube content is about 8 wt%, which can be an optimal sensitive material choice for a flexible magnetic sensor.
In this work, the advanced all solid-state block copolymer electrolytes (SBCPEs) for lithium-ion batteries with double conductive phases, poly(ethylene oxide)-b-poly(trimethyl-N-((2-(dimethylamino)ethyl methacrylate)-7-propyl)-ammonium bis(trifluoromethanesulfonyl) imide) (PEO-b-PDM-dTFSI)/LiTFSI, were fabricated, in which the charged PDM-dTFSI block contained double quaternary ammonium cations and the PEO block was doped with LiTFSI. The disordered (DIS) and ordered lamellae (LAM) phase structures were achieved by adjusting the composition of the block copolymer and the doping ratior. In addition, the presence of the hard PDM-dTFSI block and the formation of the LAM phase structure resulted in a good mechanical strength of the solid PEO-b-PDM-dTFSI/LiTFSI electrolyte, and it could maintain a high level of 104Pa at 100 °C, which was around 10,000 times stronger than that of the PEO/LiTFSI electrolyte. Based on the good mechanical and electrochemical properties, the PEO-b-PDM-dTFSI/LiTFSI SBCPE exhibited excellent long-term galvanostatic cycle performance, indicating the strong ability to suppress lithium dendrites.
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