Transport of hydrogenic species in crystalline oxides: radiation and electric-field-enhanced diffusion

Abstract

Thermal diffusion of protons, deuterons and tritons forming OH−, OD− and OT− radicals respectively was monitored by infrared absorption measurements in MgO, Al2O3, LiNbO3 and TiO2 single crystals. The electric charge and/or ionic radius is shown to be more important than mass in affecting the diffusion behaviour in these oxides. The influence of selected impurities and crystal orientation on the diffusion parameters was also investigated. Thermal diffusion of protons occupying substitutional anion vacancies (hydride ions) or [H−]+ centres was studied in thermochemically reduced MgO crystals. Simulations using an ab initio Hartree–Fock cluster approach indicate that the mobile defect is more compatible with the H− ion than with the proton.