Exploring the Thermal and Mechanical Properties of Semi Metallic XCr₂S₄ (X: Ag, Au) Monolayers

The synthesis of non-layered two-dimensional materials is crucial due to the ability to precisely control their composition and structural features. Recently, a non-layered two-dimensional material with the empirical formula AuCrS₂ was synthesized [Nano Letters, 24 (2024) 2308]. Inspired by this experimental report, we predict two thermodynamically and dynamically stable two-dimensional materials with the empirical formula XCr₂S₄ (X=Ag, Au) using density functional theory. These materials are semi-metallic and exhibit high mechanical resistance, with a Young's modulus of 200 N/m. Utilizing machine learning, we calculated the phonon thermal conductivity of these materials. At room temperature, their thermal conductivity is approximately 45 W/mK, indicating a lower phononic thermal conductivity compared to transition metal dichalcogenide monolayers and Maxene. Given their semi-metallic nature, we also investigated their electronic thermal conductivity by calculating the transmission coefficient in the linear response regime. Our findings indicate that the electron contribution to heat transfer is about 5%. The combination of high mechanical flexibility, semi-metallic nature, and low thermal conductivity suggests these materials have significant potential for use in rechargeable ion batteries, electrodes, and sensors.