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 and ε2, deviate strongly from the arithmetic means 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 the 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.