Effect of grain boundaries on the work function of hafnium: A first-principles investigation

Abstract

Hafnium (Hf) has been used as a cathode material for thermionic emission in high temperature environments for a long time. However, the effect of grain boundaries (GBs) on its work function has not been reported. In this work, by using first-principles calculations, we find that the introduction of GBs would reduce the work function of Hf surface as compared with that of the perfect crystal, and by increasing the distance between two grain boundaries, the work function converges gradually to the value of monocrystalline Hf. By analyzing the surface atomic structure and charge density distribution, we find that the reduced work function of GB-containing structures originates from the increase of atomic distance and the changes of atomic coordination environments at the GB region, which results in redistribution of electrons and enhances the electronic density of states at the Fermi level.