High-entropy ceramic thin films; A case study on transition metal diborides

High-entropy materials often outperform their lower-entropy relatives in various aspects, such as thermal stability and fracture toughness. While there are extensive research activities in the field of high-entropy alloys, comparably little is performed for high-entropy ceramics, and especially for high-entropy diborides. Here we show, that not only the hardness of ZrB₂ layers can be improved from 43.2 ± 1.0 GPa to 45.8 ± 1.0 GPa to 47.2 ± 1.8 GPa through the formation of solid solution ternary diborides (Zr_0.61Ti_0.39B₂) and high-entropy diborides (Zr_0.23Ti_0.20Hf_0.19V_0.14Ta_0.24B₂), respectively, but especially their thermal stability against structural rearrangements and decomposition towards the constituting binary diborides.