Breakthrough in Microwave Absorption for Long‐Term Thermal Cycling (HfZrTiCe‐Ln)C/SiC With Dual‐Heterogeneous Interfaces

The dielectric loss mechanism for the broadband absorption performance of carbide ceramics has not yet been elucidated, due to the long‐standing difficulty in obtaining zero‐amorphous carbon interfaces. Here, we applied a machine learning compositional design system to accelerate the discovery of high‐performance materials. An interface engineering strategy was then proposed to understand high‐performance microwave absorbers based on (HfZrTiCe‐La/Nd/Gd)C‐ceramic composites, which was assisted by using lattice matching effect of SiC and variable valence rare earth elements. The mono‐heterogeneous interface of SiC/HEC composite without carbon phases, formed via diffusion‐driven solid‐phase reactions, were first observed. HRTEM observations and MD simulations confirmed that SiC/C/HEC formed dual‐heterogeneous carbon interfaces (SiC‐graphite and HEC‐amorphous carbon). The latter composites showed superior effective absorption bandwidth and reflection loss in the frequency range of 2–18 GHz compared to the former composites. Specifically, effective absorption bandwidth of the SiC/C/HEC‐La was 7.5 GHz at 2.2 mm, which is 15 times that of SiC/HEC‐La. This was owing to the former with 73.14% proportion of sp3/sp2 carbon bonds and a higher interfacial carbon content, which improved dielectric loss and impedance matching. The dual‐heterogeneous carbon interface, having over half of the disordered carbon phase ( I D / I G = 1.14) is the key factor.