Hydrogen Isotope Absorption in Unary Oxides and Nitrides with Anion Vacancies and Substitution

Abstract

The absorption states of hydrogen isotopes in various ceramic materials were investigated by density functional theory. For pristine ceramic materials, main-group oxides do not form any bond with a hydrogen atom. However, transition metal oxides form hydroxyl groups and absorb hydrogen atoms. Main-group and transition metal nitrides form ionic bonds between a hydrogen atom and the surrounded cation. For anion-deficient ceramic materials, hydrogen atoms are negatively charged because of excess electrons induced by anion vacancies, and ionic bonds form with the surrounded cation, which stabilizes the hydrogen absorption state. N substitutional doping into oxides introduces an electron hole, while O substitutional doping into the nitrides introduces an excess of electrons. Therefore, hydrogen isotopes form covalent bonds in Nsubstituted oxides, and form hydride ions in O-substituted nitrides. Thus, Al 2 O 3 , SiO 2 , CrN, and TiN are promising materials as hydrogen permeation barriers.[a] T.

Chemical Interaction of Hydrogen Radicals (H*) with Transition Metal Nitrides

“…For example, under standard temperature and pressure, Δ G for denitridation of TiN by H* under the formation of ammonia (NH 3 ) is calculated to be negative . However, H* are likely to preferentially form bonds with the Ti cations in TiN, , making the formation of volatile NH 3 less likely. Therefore, in this work, we investigate how the hydrogenation pathway defined by the work function and the thermodynamic favorability for forming volatile species influences the reduction of TMN thin films in a H* environment at elevated temperature (700 °C).…”