High Pressure Phase of LiAlO2: A First Principles Study

Abstract

The homogeneous structural phase transition between the natural and high-pressure forms of LiAlO2, i.e., γ-LAO and δ-LAO, were investigated by using first principles calculations. For the exchange-correlation functional, the generalized-gradient approximation (GGA) was used in comparison with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. The projector augmented wave (PAW) method was used to allow a relatively low-energy cutoff plane wave expansion outside the core region while maintaining the complicated description of the wave function near the core region. Our calculations showed that both HSE and GGA calculations provided comparable energetic properties. For the electronic properties, the HSE calculations do not suffer from band gaps underestimations but require much more computation demand. The HSE calculations showed that, under hydrostatic pressure, the natural phase γ-LAO is in energetic equilibrium with the high-pressure phase δ-LAO at 2.3 GPa. The calculated equilibrium phase pressures are in a reasonable agreement with the experimental transformation pressure (2 GPa) obtained by an anvil cell technique [J. Solid State Chem. 188, 6 (2008)]. However, the transformation pressure obtained by a shock recovery technique [J. Solid State Chem. 177, 5 (2004)] is much higher (9 GPa). The large difference in the transformation pressure obtained by different experimental techniques could be attributed to the energetic transformation barrier between the two phases. Based on HSE calculations, the enthalpy barrier for the homogeneous transformation between the two phases at the phase equilibrium pressures is 1.8 eV. The band structures and the partial density of states of both γ-LAO and δ-LAO at the ambient pressure are also presented.