Pressure effects on the ionic transport properties of LiNH2

Abstract

The ionic transport properties of LiNH₂ under high pressures up to 30.8 GPa are systematically studied with alternate-current impedance spectra measurements and first-principles calculations. Two discontinuous changes of the electrical parameters can be found at approximately 12.0 and 20.0 GPa, which are attributed respectively to the pressure-induced structural phase transitions from the tetragonal phase to the monoclinic phase and the change of the transportation mechanism from mixed ionic and electronic conduction to pure ionic conduction. The conductivity of LiNH₂ is decreased by one order of magnitude under high pressures due to the decreased migration rate of Li⁺ ions. Relaxation loss is found in LiNH₂, which is caused by the long-distance diffusion of Li⁺ ions during the orientation polarization. The calculated ionic-migration potential barriers indicate that the energy required for Li⁺ ion migration increases with increasing pressure. The decrease in the amount of non-local electrons in the monoclinic phase led to the disappearance of electronic conduction after 20.0 GPa.