Anisotropic thermal expansion in high-entropy multicomponent AlB2-type diboride solid solutions

High-entropy (HE) ultra-high temperature ceramics have the chance to pave the way for future applications propelling technology advantages in the fields of energy conversion and extreme environmental shielding. Among others, HE diborides stand out owing to their intrinsic anisotropic layered structure and ability to withstand ultra-high temperatures. Herein, we employed in-situ high-resolution synchrotron diffraction over a plethora of multicomponent compositions, with four to seven transition metals, with the intent of understanding the thermal lattice expansion following different composition or synthesis process. As a result, we were able to control the average thermal expansion (TE) from 1.3 x 10(-6) to 6.9 x 10(-6) K-1 depending on the combination of metals, with a variation of in-plane to out-of-plane TE ratio ranging from 1.5 to 2.8.

Automated summary

High-entropy (HE) ultra-high temperature ceramics, particularly HE diborides, have great potential for energy conversion and extreme environmental shielding due to their intrinsic anisotropic layered structure and ability to withstand ultra-high temperatures. In this study, we used high-resolution synchrotron diffraction to investigate the thermal lattice expansion in various multicomponent compositions. The results showed that the average thermal expansion and the ratio of in-plane to out-of-plane expansion could be controlled by the combination of metals used.