Magnesium ion dynamics in Mg(BH4)2(1−x)X2x (X = Cl or AlH4) from first-principles molecular dynamics simulations

Abstract

We use large-scale first-principles molecular dynamics simulations to find possible ways to make magnesium dication conductors based on Mg(BH₄)₂. The Mg atoms are confined in a tetrahedral cage of BH₄ groups and coordinated by eight hydrogen atoms from these groups. These Mg atoms do not move outside the cage either in high- or low-temperature phases. After introducing larger-sized AlH⁻₄ anions by substitution of 20% BH⁻₄, the Mg atoms are able to move outside the cage with coordination from hydrogen atoms of BH⁻₄ located outside the cage. Substitution by Cl⁻ and I⁻ anions did not allow large Mg movements.