Ultrasonic Field Induces Better Crystallinity and Abundant Defects at Grain Boundaries to Develop CuS Electromagnetic Wave Absorber

Ultrasonic field (USF) is widely used to regulate the intrinsic properties of materials that are not applied in electromagnetic wave (EMW) absorption. One reason is that the lack of a response mechanism for the materials to USF hinders the expansion of their EMW absorption performance. Therefore, to address this issue, a series of CuS nanoparticles with diverse anions are constructed in the presence or absence of USF. The ultrasonic-induced cavitation effect can significantly promote CuS crystallization and lead to the accumulation of S defects at the grain boundaries (GBs). Furthermore, the S defects at the GBs are easily oriented and arranged, allowing the polarization relaxation retention to be maintained at 10 wt%. Consequently, the CuS with a nitrate precursor under USF shows an optimum effective absorption bandwidth (EAB) of 10.24 GHz at a thickness of 3.5 mm, which is 228.6% more than that without the USF. CuS with a chloride precursor also achieves an EAB of 3.92 GHz, even at a considerably low filler ratio. Thus, this study demonstrates the response mechanism of diverse anions to the USF for the first time and provides a novel technique to optimize the EMW absorption performance of semiconductors.