Probing alloying effects of rare earth and transition metal on surface energy and work function of ZrO 2 : A First-principles study

Lowering work function ( Phi ) is considered to be an effective pathway to activate electron transpiration cooling (ETC) thermal mechanism to solve the thermal barrier problem of hypersonic vehicles. However, little study has been carried out for an in-depth understanding of alloying effects on the work function of ultra -high temperature heatshield materials. In this study, we performed a comprehensive investigation concerning the alloying effects on the surface stability, work function, and electronic structure of ZrO 2 as the base object by employing first principles. Up to 22 elements including all the lanthanides (LA) and part of transition metals (TM) are considered for doping the ZrO 2 (101) surface. Our results demonstrate that although the LA/TM reduces the surface stability, appropriately increasing the environmental oxygen concentration could increase the surface stability. But excessive oxygen concentration may result in the instabilities of the LA/TM-doped ZrO 2 (101) surface. La, Ce, and Pr amongst the LA elements significantly reduce the Phi while Yb and Lu do in opposite. For the TM elements, Nb, Ta, and V reduce the Phi while Sc , Ti, and Y yield the opposite effect. In view of low Phi and high melting temperature ( T m ), Ta, Nb, or V provides a promising candidate for tuning the ETC mechanism of ZrO 2 . Based on the analysis of electronic configurations, the influence mechanism of alloying elements is traceable from the chemical bonding and the geometry of charge density.