Optical responses from High Entropy Alloys : experimental results and perspectives

Abstract

High-entropy alloys (HEAs) combine five or more elements in near-equiatomic ratios, opening an immense compositional space whose optical behaviour is still largely unknown. Phase-modulated ellipsometry on bulk CrMnFeCoNi (Cantor) shows that its intrinsic optical constants n, k, ε1, ε2 deviate strongly from the arithmetic mean of the constituent elements—by up to a factor of two beyond 1 µm—yet the derived functional responses, reflectance R and absorption coefficient α, are reproduced to within ~20 %. Cantor nanoparticles have been produced by nanosecond electric discharges in liquid nitrogen. Dark-field spectroscopy and Mie calculations reveal a dominant scattering mode near 100 nm that red-shifts and broadens with increasing size; the steady-state photothermal rise calculated from absorption cross-section σabs falls between those of the constituent pure metals.Generalising the averaging rule, we compute proxy values of R and α for 10 994 density-functional-theory-predicted HEAs. Successive optical, thermal and resource filters condense the space to 58 candidates at 355 nm and eight refractory alloys at 1064 nm, illustrating a “sustainable-by-design” route for future HEA photonics

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