Pressure-induced metal-insulator and spin-state transition in low-valence layered nickelates

Ab initio calculations predict a metal-insulator transition at zero temperature to occur in La₄Ni₃O₈ at moderate pressures as a result of a pressure-induced spin-state transition. The spin-state transition that is seen at 105 K at ambient pressure, from a low-temperature high-spin state to a high-temperature low-spin state, has been observed to be shifted to lower temperatures as pressure is applied. From our calculations, we find that a smaller unit cell volume favors the metallic low-spin state, which becomes more stable at 5 GPa. Similar physics appears in the related compound La₃Ni₂O₆, but on a different energy scale, which may account for why the transition has not been observed in this material.