First principles study of LiAlO₂: new dense monoclinic phase under high pressure

In this work, we have systematically explored the crystal structures of LiAlO₂ at high pressures using crystal structure prediction method in combination with the density functional theory calculations. Besides the reported α, β, γ, δ and ε-phases, here we propose a new monoclinic ζ-LiAlO₂ (C2/m) structure, which becomes thermodynamically and dynamically stable above 27 GPa. It is found that the cation coordination number increases from 4 to 6 under compression. Consisting of the compact {LiO₆} and {AlO₆} octahedrons, the newly-discovered ζ-phase possesses a very high density. Further electronic calculations show that LiAlO₂ is still an insulator up to 60 GPa, and its bandgap increases upon compression. The present study advances our understanding on the crystal structures and high-pressure phase transitions of LiAlO₂ that may trigger applications in multiple areas of industry and provoke more related basic science research.