Cr ₂ AlC: A High‐Temperature Transparent Conducting Ceramic

ABSTRACT Transparent conductors with high conductivity, optical transparency, and thermal stability are critical for next‐generation optoelectronic devices, yet such materials are scarce. Here, we demonstrate that epitaxial Cr ₂ AlC(0001)/Al ₂ O ₃ (0001) layers exhibit a unique combination of these properties. The optical transmittance of ultrathin layers reaches 85% at 900 nm and remains above 21% across the near‐infrared (NIR)ultraviolet (UV) range, in good agreement with first‐principles optical properties predictions which reveal a small plasma frequency and a low cross‐section for interband transitions. Cr ₂ AlC has a room‐temperature bulk resistivity ρ _o = 42.5 µΩcm and an exceptionally small resistivity scaling with a negligible (<4%) resistivity increase down to 10 nm, an effective bulk electron mean free path λ < 2 nm at both 295 and 77 K, and a temperature‐independent effective ρ _o λ < 3 × 10 ⁻¹⁶ Ωm ² that is smaller than that of all known elemental metals. An 11.1‐nm‐thick Cr ₂ AlC layer achieves a benchmark Φ _TC ≈ 0.004 Ω ⁻¹ in the near infrared (900 nm), comparable to state‐of‐art transparent conductors including ultra‐thin silver and carbon‐based materials. These results, in combination with the known oxidation stability to 1073–1373 K, establish Cr ₂ AlC as a uniquely robust, high‐temperature stable and scalable transparent conductor, paving the way for advanced extreme‐environment optoelectronics and photonics.