Theoretical screening of rare earth and transition metals for tuning surface electron emission of ZrB2

Abstract

One promising strategy to improve electron transpiration cooling (ETC) in hypersonic vehicles is to reduce the work function (Φ). Yet, not much research has been done on how alloying affects the Φ modulations of heat shield materials at extremely high temperatures. This research employs first-principles to investigate the comprehensive influences of alloying on the ZrB₂(0001) surface, focusing on 22 elements comprising all of the lanthanides (LA) and a few particular transition metals (TM). Our results indicate that while doping LA/TM impairs surface stability except doping Gd, Nd and Sc, elevated environmental boron levels can ameliorate this issue. Doping with lanthanides leads to varying degrees of Φ reduction. Among them, La, Ce, and Pr exhibit a significant decrease in Φ values. Transition metals like Y and Sc lower Φ, while Nb, Hf, and Ta have the contrary results. With regard to the low Φ and a high melting temperature (T_m) point, La, Y, or V are promising candidates for optimizing ETC in ZrB₂. The electronic structure analyses reveal the underlying mechanisms through chemical bonding and charge density geometry.