Correlation governs the impurity (Ti, Zr, Hf) diffusion in face−centered cubic iridium through first−principles calculation

Abstract

Solid state diffusion depends on many factors, including crystal structure, vacancy concentration, energy barrier, jump frequency, correlation, etc.. In this work, those factors were systematically investigated for dilute IVB transition metals X (X = Ti, Zr, Hf) diffusion in face−centered cubic (FCC) Ir using first−principles calculations together with quasi−harmonic thermodynamics, climb−image nudged elastic band (CINEB), and five−frequency diffusion model. The results show that correlation which is often neglected in low melting point metals and alloys plays a key role in the impurity diffusion in Ir. The correlation factor which ranges from 10−13 at 500 K to 10−1 at 2000 K overturns the contributions from other factors, like vacancy concentration, energy barrier, and jump frequency. The diffusion coefficient of Ir−X (X = Ti, Zr, Hf) systems follows DHf > DZr > DTi, different from our traditional knowledge. Our findings not only give a good recount to the counterintuitive experimental phenomena in Ir oxidation resistance coating or ultrahigh−temperature Ir-based superalloys, but also provide valuable diffusion data for rational design of Ir-based materials for applications with harsh environment.