Pressure-induced spin crossover in disordered α-LiFe O2

Structural, magnetic, and electrical-transport properties of α-LiFeO2, crystallizing in the rocksalt structure with random distribution of Li and Fe ions, have been studied by synchrotron x-ray diffraction, Fe57 Mössbauer spectroscopy, and electrical resistance measurements at pressures up to 100 GPa using diamond anvil cells. It was found that the crystal structure is stable at least to 82 GPa, though a significant change in compressibility has been observed above 50 GPa. The changes in the structural properties are found to be on a par with a sluggish Fe3+ high- to low-spin (HS-LS) transition (S=5/2→S=1/2) starting at 50 GPa and not completed even at ∼100 GPa. The HS-LS transition is accompanied by an appreciable resistance decrease remaining a semiconductor up to 115 GPa and is not expected to be metallic even at about 200 GPa. The observed feature of the pressure-induced HS-LS transition is not an ordinary behavior of ferric oxides at high pressures. The effect of Fe3+ nearest and next-nearest neighbors on the features of the spin crossover is discussed.