Electron- or Hole-Assisted Reactions of H Defects in Hydrogen-Bonded KDP

Abstract

We present an ab initio study of the stability and defect reactions of neutral and charged H interstitial (${\mathrm{H}}_{i}$) and H vacancy (${\mathrm{H}}_{v}$) in ${\mathrm{K}\mathrm{H}}_{2}{\mathrm{P}\mathrm{O}}_{4}$ (KDP). We find that while there is no interaction between the neutral ${\mathrm{H}}_{i}$ and the host, the addition of an electron leads to the ejection of a H host atom and the subsequent formation of an interstitial ${\mathrm{H}}_{2}$ molecule and a ${\mathrm{H}}_{v}$. In sharp contrast, the addition of a hole results in the formation of a hydroxyl bond. Thus, ${\mathrm{H}}_{i}$ in both charged states severs the H-bonded network. For the ${\mathrm{H}}_{v}$, the addition of a hole leads to the formation of a peroxyl bridge. The neutral ${\mathrm{H}}_{i}$ and the positively charged ${\mathrm{H}}_{v}$ induce states in the gap. The results elucidate the underlying atomic mechanism for the defect reactions suggested by experiment.