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 with tetrakis(dimethylamino)zirconium(IV), followed by pyrolysis and annealing. Advanced characterization methods combined with first-principles calculations via 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 an 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, ZrC_xN_1−x transforms into ZrB₂, forming SiC/ZrB₂ multiphase ceramic nanocomposites. With the incorporation of Zr, SiZrBCN-16, after annealing at 1600 °C, exhibits excellent EMW absorption 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 the free carbon network, DFT analysis revealed two primary dielectric loss mechanisms that result 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 atomic disparity across the interface at the ZrC(001)/β-Si₃N₄(001) and ZrN(100)/SiC(110) boundaries induce electronic reconstruction and charge separation.

Dense monolithic (Ti,Zr,Hf,Ta)CN/SiCN ceramic nanocomposites are prepared via the pyrolysis of novel (Ti-,Zr-,Hf-,Ta)-containing single-source precursors (SSPs) and spark plasma sintering (SPS) with a high heating rate. The synthesis, polymer-to-ceramic transformation, and structural evolution of the nanocomposites are thoroughly investigated. The mechanical properties and air‒plasma ablation resistance of the nanocomposites are also investigated. The results show that the nanocomposites are characterized by multicomponent (Ti,Zr,Hf,Ta)CN nanoparticles uniformly distributed within the SiCN matrix (composed of SiC and/or Si₃N₄). The phase composition and molar ratios of metal elements within the (Ti,Zr,Hf,Ta)CN nanoparticles can be precisely controlled via the molecular design of the SSPs and control of the reaction sequence. The nanocomposites exhibit excellent mechanical properties, with hardness, Young’s modulus, and flexural strength of 35–37, 357–417, and 532–603 MPa, respectively, owing to multicomponent solid solution strengthening and interface strengthening. The linear ablation rate of (Ti_0.1Zr_0.3Hf_0.5Ta_0.1)CN/SiCN with approximately 80 wt% (Ti_0.1Zr_0.3Hf_0.5Ta_0.1)CN at 2200 °C is 0.033 μm/s, which is 2 orders of magnitude lower than those of other multicomponent ultrahigh-temperature ceramics (UHTCs) under similar conditions. The excellent ablation resistance can be attributed to the nanoscale grain size of the multicomponent (Ti,Zr,Hf,Ta)CN phase and its excellent homogeneity within the SiCN matrix, which enables the formation of a continuous and dense oxide layer with a Hf(Zr,Ti)O₂ skeleton filled with SiO₂/Ta₂O₅.

Dense monolithic (Ti,Zr,Hf)C/SiC ceramic nanocomposites with four different molar ratios of metallic elements in the (Ti,Zr,Hf)C phase (i.e., Ti : Zr : Hf = 1 : 1 : 1, 2 : 3 : 5, 2 : 3 : 3, and 1 : 2 : 1) were prepared upon pyrolysis of novel (Ti,Zr,Hf)-containing single-source precursors (SSPs), followed by spark plasma sintering (SPS). A thorough characterization was conducted to elucidate the synthesis of the SSPs, polymer-to-ceramic transformation, chemical/phase compositions, and microstructure of the SiTiZrHfC-based ceramics. The results revealed the feasibility of synthesizing nanocomposites with high (Ti,Zr,Hf)C contents using the SSP method. These nanocomposites were characterized by a unique microstructure with in situ generated (Ti,Zr,Hf)C@C core–shell nanoparticles homogeneously mixed with β-SiC. The ablation behavior of the nanocomposites was evaluated on an air-plasma device for 60 s. Impressively, the nanocomposites exhibited excellent ablation resistance, and the lowest linear ablation rate reached −0.58 μm/s at 2200 °C. Notably, the ablation resistance can be dramatically improved by precisely tailoring the atomic ratios of metal elements within the (Ti,Zr,Hf)C phase via the molecular design of the SSPs. The formation of a multiple-oxide layer with both a high-melting-point phase ((Ti,Zr,Hf)O₂) and low-melting-point phases ((Zr,Hf)TiO₄) and glassy SiO_2, as well as their structure, played a critical role in the enhanced ablation resistance. The uniform distribution of the high-melting-point (Ti,Zr,Hf)O₂ nano/microparticles throughout the glassy SiO₂ matrix significantly enhanced the viscosity and stability of the oxide layer by the pinning effect, offering superior protection against the ingress of oxygen atoms and excellent resistance to mechanical erosion.

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 (Cu₃Si). 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/Cu₃Si/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_min) of the SiCN/Cu/Cu₃Si/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 in situ formed unique network, which was constructed with Cu and Cu₃Si nanoparticles connected by ring-like carbon ribbons within the SiCN matrix.