Physical Properties and Their Influence on Irradiation Damage in Metal Diborides and in High-Entropy Materials

Physical properties and irradiation damage in four transition metal diborides (TM-diborides) are investigated: one high-entropy diboride (Hf_0.2Nb_0.2Ta_0.2Ti_0.2Zr_0.2)B₂ and three subsets of quaternary diborides. Surprisingly, instead of being generally classified as ceramic materials, the predominant mechanism for heat conduction is through electrons. The irradiation response of these TM-diborides under ion irradiation at room temperature has been investigated using 10 MeV Au ions to fluences up to 6 × 10¹⁵ Au cm⁻². Black dot dislocation loops are visible at low doses, whereas dislocation networks are observed with increasing fluence. While up to ~ 4% volume expansion has been determined in these diborides, the crystalline structure remains stable under room-temperature irradiation, preserving the hexagonal AlB₂ phase. Perspectives of chemical disorder resulting from various TMs in high-entropy materials, along with their associated physical properties and influence on irradiation damage, are discussed in terms of the number of valence electrons, atomic mass, and volume.