Atomic-scale elucidation of attenuation mechanisms underlying exceptional electromagnetic wave absorption of SiZrBCN ceramic nanocomposites

To elucidate the atomic-scale mechanisms governing electromagnetic wave (EMW) attenuation in polymer-derived ceramics, a SiZrBCN ceramic nanocomposite was prepared via chemical modification of polyborosilazane using tetrakis(dimethylamino)zirconium (IV), followed by pyrolysis and annealing. Advanced characterization methods combined with first-principle calculations using density functional theory (DFT) were employed to investigate the structural evolution, dielectric properties and attenuation mechanisms of the nanocomposites. The results show that after pyrolysis at T≤1400 °C, the SiZrBCN is in amorphous state. As the annealing temperature increases, ZrC_xN_1-x, SiC, and β-Si₃N₄ initially precipitate at 1500 °C. When the temperature increases to 1800 °C, the ZrC_xN_1-x transforms into ZrB₂ forming a SiC/ZrB₂ multiphase ceramic nanocomposites. With the incorporation of Zr, the SiZrBCN-16 after annealing at 1600 °C exhibits excellent EMW absorbing performance, achieving a maximum effective absorption bandwidth of 6.03 GHz (thickness: 1.65 mm) and a minimum reflection loss of -44.1 dB (thickness: 1.9 mm). In addition to the conductive loss caused by free carbon network, DFT analysis identified two primary dielectric loss mechanisms which results in exceptional absorbing performance: (1) electronegativity-driven charge separation in ZrC_xN_1-x solid solutions facilitates the formation of electric dipoles; (2) interfacial lattice distortion and the atomic disparity across the interface at ZrC(001)/β-Si₃N₄ (001) and ZrN(100)/SiC(110) boundaries induce electronic reconstruction and charge separation.