Wireless surface acoustic wave (SAW) sensors hold great promise for in-situ, real-time monitoring and accurately assessing the health status of hot-end components. However, the thin-film electrode as the SAW sensor core unit with excellent high-temperature conductivity, stability, and oxidation resistance is still a challenge, especially in ultra-high temperature harsh environments. Herein, we employed polymer-derived ceramic approach to fabricate smooth and dense SiHfBCN ceramic coating on the YCa₄O(BO₃)₃/BN substrate. The composition, microstructural evolution, and room temperature and high-temperature electrical conductivity of SiHfBCN ceramic coatings were investigated to reveal the mechanism for controlling electrical conductivity. The results indicate that the electrical conductivity of the SiHfBCN ceramic coating pyrolyzed at lower temperature of 1200 °C reaches an impressive high value of 291.55 S·m^-¹ at 1200 °C in argon. Importantly, the result also demonstrates that the coating has remarkable high-temperature conductivity, excellent repeatability and durability. Therefore, the SiHfBCN ceramic coatings exhibiting typical semiconducting behavior highlights their potential as the thin-film electrode of SAW high-temperature sensors in high temperature extreme environments.

To further improve the performance of binders, a SiHfBCN-based high-temperature resistant adhesive was successfully synthesized by Polymer-Derived Ceramics (PDC) route using TiB₂, Polysiloxane (PSO) and short SiC nanowires as fillers. The effect of short SiC nanowires on the adhesive strength at room temperature and high temperature, as well as the reinforcing mechanism was studied. Compared with the adhesive without SiC nanowires, after curing (at 170 ℃) and pyrolysis (at 1000 ℃) in air, the appropriate adding of SiC nanowires upgrades the room temperature and high temperature (at 1000 ℃ in air) adhesive strength to (12.50 ± 0.67) MPa (up by about 32%) and (13.11 ± 0.79) MPa (up by about 106%), respectively. Attractively, under the synergistic impact of the nanowire bridging, nanowire breaking, nanowire drawing and crack deflection, the optimized adhesive exhibits multi-stage fracture, causing the increscent fracture displacement.

For the first time, ZrC-ZrB₂-SiC ceramic nanocomposites were successfully prepared by a single-source-precursor route, with allylhydridopolycarbosilane (AHPCS), triethylamine borane (TEAB), and bis(cyclopentadienyl) zirconium dichloride (Cp₂ZrCl₂) as starting materials. The polymer-to-ceramic transformation and thermal behavior of obtained single-source precursor were characterized by means of Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). The results show that the precursor possesses a high ceramic yield about 85% at 1000 ℃. The phase composition and microstructure of formed ZrC-ZrB₂-SiC ceramics were investigated by means of X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Meanwhile, the weight loss and chemical composition of the resultant ZrC-ZrB₂-SiC nanocomposites were investigated after annealing at high temperature up to 1800 ℃. High temperature behavior with respect to decomposition as well as crystallization shows a promising high temperature stability of the formed ZrC-ZrB₂-SiC nanocomposites.