Thermal Ionization of Hydrogen in Hydrous Olivine With Enhanced and Anisotropic Conductivity

Trace amounts of hydrogen in olivine can significantly increase its conductivity. However, the conduction mechanism in hydrous olivine is still unclear, which hinders the in-depth understanding of the high conductivity structures of the asthenosphere. We investigate the proton conduction mechanism in hydrous olivine using ab initio calculations. Several models were examined using climbing image nudged elastic band and ab initio molecular dynamics methods. We found that hydrogen trapped at the Mg (or Fe) defect is more mobile than hydrogen trapped at the Si defect. At high temperature, we observed the ionization of hydrogen from cation defects leading to high and anisotropic proton conductivity along the [100] direction. The highly anisotropic conductivity caused by thermal ionized hydrogen at high temperature explains the experimental observations on olivine single crystals.