Microstructural evolution and electromagnetic wave absorbing performance of single-source-precursor-synthesized SiCuCN-based ceramic nanocomposites
Jincan Yang, Qingbo Wen, Bo Feng, Yalei Wang, Xiang Xiong
Abstract
Copper (Cu)-containing single-source precursors (SSPs) for the preparation of SiCuCN-based ceramic nanocomposites were successfully synthesized for the first time using polysilazane (PSZ), copper(II) acetate monohydrate (CuAc), and 2-aminoethanol via nucleophilic substitution reactions at silicon (Si) centers of PSZ. The synthesis process, polymer-to-ceramic transformation, and high-temperature microstructural evolution of the prepared ceramics were characterized. Dielectric properties and electromagnetic wave (EMW) absorbing performance of the ceramics were investigated as well. The results show that the polymer-to-ceramic transformation finishes at ca. 900 ℃, and Cu nanoparticles are homogeneously distributed in a SiCN matrix, forming a SiCN/Cu nanocomposite. After annealing at 1200 ℃, the Cu nanoparticles completely transform into copper silicide (Cu<sub>3</sub>Si). Interestingly, the thermal stability of the Cu nanoparticles can be strongly improved by increasing the free carbon content, so that a part of metallic Cu nanoparticles can be detected in the ceramics annealed even at 1300 ℃, forming a SiCN/Cu/Cu<sub>3</sub>Si/C nanocomposite. Compared with SiCN, the SiCuCN-based nanocomposites exhibit strongly enhanced dielectric properties, which results in outstanding EMW absorbing performance. The minimum reflection coefficient (RC<sub>min</sub>) of the SiCN/Cu/Cu<sub>3</sub>Si/C nanocomposites annealed at 1300 ℃ achieves −59.85 dB with a sample thickness of 1.55 mm, and the effective absorption bandwidth (EAB) broadens to 5.55 GHz at 1.45 mm. The enhanced EMW absorbing performance can be attributed to an <i>in situ</i> formed unique network, which was constructed with Cu and Cu<sub>3</sub>Si nanoparticles connected by ring-like carbon ribbons within the SiCN matrix.