Fabrication and high temperature electrical conductivity of polymer-derived SiHfBCN ceramic coating: A wireless surface acoustic wave sensor material?

The hot-end components of aircraft and spacecraft are generally suffered from extreme service environments, which are characterized by thermo-oxygen coupling, high-temperature oxidation, erosion, and vibration. Wireless surface acoustic wave (SAW) sensors, as a new type of intelligent sensor, hold great promise for in-situ, real-time monitoring of parameters such as temperature, heat flow, and strain on the surface of these components. This capability is crucial for accurately assessing the health status of hot-end components and ensuring flight safety. Consequently, the thin-film electrode of the sensor core unit must exhibit excellent high-temperature conductivity, stability, and oxidation resistance. However, due to the poor wettability with substrate and the large atomic diffusion coefficient, the metal film such as Pt, Ti and Cr is prone to agglomeration at high temperature, which limits their application in harsh environments. On the contrary, ceramic possess excellent stability and longtime durability at high temperatures. As reported, Tin-doped indium oxide (ITO) thin-film electrode is known for high-temperature stability, oxidation resistance and excellent semiconductor behavior. Nevertheless, structural damage leading to the failure of conductivity at 1100 °C is the obvious drawback of these ceramic due to a limited maximum operating temperature, which are disadvantage for electrical properties of the ceramic. Moreover, ultra-high temperature ceramics (UHTCs), such as HfC, HfN, and HfB₂, exhibit electrical conductivity on the order of 10⁴ S·cm^-¹, which makes them very promising as thin-film electrodes for SAW sensing applications in harsh environments. However, it is difficult to obtain stable ceramic coatings because of a possibility of oxidation at a low temperature, such as HfB₂ is easily oxidized at 800 °C. Moreover, the conventional method of UHTC coatings such as chemical vapor deposition (CVD) method and magnetron sputtering method exists the problems of slow growth rate and longtime preparation, limiting their application in harsh environments. Polymer-derived ceramics (PDCs) method has attracted great attention because of the advantages of rapid preparation of film and adjustable thickness of film. However, the maximum test temperature of the high-temperature conductivity of the existing PDC SiOC, SiCN and SiBCN ceramics is 1000 °C, and most of the ceramics are bulk ceramics, so the feasibility of their application as high-temperature thin film electrodes is not proven. PDC SiHfBCN ceramics have been proved promising ceramics for ultra-high-temperature applications due to excellent high-temperature stability and oxidation resistance up to 1500 °C. The high-temperature electrical conductivity of PDC SiHfBCN ceramic coating, especially above 1000 °C, have not been reported yet.

Recently, a team of material scientists led by Xingang Luan from Northwestern Polytechnical University, China first reported the fabrication, composition, microstructural evolution, and room temperature and high-temperature electrical conductivity. The relationship between microstructure and electrical conductivity at high temperatures was established to explain the conductive mechanism for the first time.

The team published their work in Journal of Advanced Ceramics (DOI: 10.26599/JAC.2024.9221011) on January 9, 2025.

“In this report, 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.” said Xingang Luan, professor of Science and Technology on Thermostructural Composite Materials Laboratory at Northwestern Polytechnical University (China), a senior expert whose research interests focus on the field of high-temperature ceramics material.

“Smooth and compact SiHfBCN ceramic coatings can be prepared by adjusting the concentration of precursor and chemical vapor deposition of BN layer on YCa₄O(BO₃)₃ substrate. After pyrolysis at different temperatures, the surface of the SiHfBCN coating is compact and flat without holes, bumps and other defects, and the coating adheres closely to the substrate without penetrating cracks or delamination. The thickness of SiHfBCN coating during pyrolysis at different temperatures is basically the same, which is not affected by the pyrolysis temperature, indicating excellent high temperature stability.” said Xingang Luan.

The resistivity of the SiHfBCN coating decreases with increasing pyrolysis temperature. The SiHfBCN ceramic coatings pyrolyzed at 1200°C has the room temperature resistivity of 1.516 ×10⁸ Ω·m, which exhibits insulation behavior. “The increase in the conductivity of the SiHfBCN coating is closely related to the Hf element and that some large band gaps in the system are transformed into Hf-N small band gaps.” said Xingang Luan.

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. The electrical conductivity of SiHfBCN ceramic coatings have almost identical and symmetrical wave patterns after 25 heating/cooling procedures “SiHfBCN ceramic coatings excellent high-temperature conductivity, outstanding repeatability and durability under high temperature, exhibiting typical semiconducting behavior.” said Xingang Luan.

Other contributors include Qinghua Zhao, Yao Li, Shaomin Gu, Xinming Xu, Dianwei He, Fang Ye, Laifei Cheng from the Science and Technology on Thermostructural Composite Materials Laboratory at Northwestern Polytechnical University in Xi’an, China; Zhaoju Yu from the Key Laboratory of High-Performance Ceramic Fibers (Xiamen University) and Xiamen Key Laboratory of Electronic Ceramic Materials and Devices in Xiamen at Xiamen University.

This work was supported by the National Natural Science Foundation of China (Nos. 52072304 and 51872246). and Creative Research Foundation of the Science and Technology on Thermostructural Composite Materials Laboratory.

About Author

Luan Xingang, holds a BSc, M.S. and Ph.D. from Northwestern Polytechnical University. He was professor and doctoral supervisor of Northwestern Polytechnical University, head of Qingdao International Science and Technology Cooperation Base for the preparation of ultra-high temperature structural Composites, director of the Joint Research Laboratory of ultra-high temperature Ceramic Matrix Composites of Northwestern Polytechnical University-Darmstadt Technical University. He presided over 2 National Natural Science Foundation projects and more than 10 other national projects, participated in 15 national Natural Science Foundation projects and other national projects, was authorized 7 national invention patents, published more than 100 academic papers. He published 1 monograph of "Simulation of Service Behavior of Ultra-high temperature Structural Composite Materials - Theory and Methods", and published English monograph "High-Temperature Thin Films and Coatings" (Protective Thin Coatings Technology Chapter 7) chapter 1. He won the second prize of Natural Science Award of the Ministry of Education, the special prize of Shaanxi Provincial Teaching Achievement Award, and the second prize of National Teaching Achievement Award.

Yu Zhaoju is a professor/doctoral supervisor at the School of Materials, Xiamen University, a "Humboldt Scholar" in Germany, and the executive deputy Director of the Key Laboratory of High-Performance Ceramic Fibers of the Ministry of Education (Xiamen University). She has been engaged in the research work of preparing high-temperature structural/functional ceramics (including ceramic fibers, powders and blocks) by PDC method for a long time, and has mastered the key evolution laws of precursor bodies in the organic to inorganic transformation process, as well as the influence laws on composition, structure and properties, and has mastered various research methods to conduct in-depth research on the composition, structure and properties of ceramics. In 2017-2018, she was awarded the "Humboldt Research Fellowship for Experienced Researchers" in Germany. In 2021, she was awarded the Engineering Ceramics Division of the American Ceramic Society, and in 2022, She received the Jubilee Global Diversity Award and the Global Ambassador Award. Currently, she serves as Cerams.Int. And J.Am.Ceram.Soc. He is an Associate Editor and serves on the editorial board of J. Adv. Ceram., Advanced Powder Materials, and Materials. He has served as Guest Editor in Chief of the European Ceramic Society J. Eur. Ceram. Soc., she has published more than 90 Sci papers as the first/corresponding author in international journals such as Nat. Mater., Prog. Mater. Sci., Acta Mater., Nanoscale, J. Mater. Chem. C, etc. She has made more than 30 invited presentations at international conferences.

About Journal of Advanced Ceramics

Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2023 IF is 18.6, ranking in Top 1 (1/31, Q1) among all journals in “Materials Science, Ceramics” category, and its 2023 CiteScore is 21.0 (top 5%) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508

About SciOpen 

SciOpen is an open access resource of scientific and technical content published by Tsinghua University Press and its publishing partners. SciOpen provides end-to-end services across manuscript submission, peer review, content hosting, analytics, identity management, and expert advice to ensure each journal’s development. By digitalizing the publishing process, SciOpen widens the reach, deepens the impact, and accelerates the exchange of ideas.