Structural and magnetic properties of LiNi_0.5Mn_1.5O₄ and LiNi_0.5Mn_1.5O_4-δ spinels: A first-principles study

Structural and magnetic properties of LiNi_0.5Mn_1.5O₄ and LiNi_0.5Mn_1.5O_4-δ are investigated using density-functional theory calculations. Results indicate that nonstoichiometric LiNi_0.5Mn_1.5O_4-δ and stoichiometric LiNi_0.5Mn_1.5O₄ exhibit two different structures, i.e., the face-centred cubic (Fd-3m) and primitive, or simple, cubic (P4₃32) space groups, respectively. It is found that the magnetic ground state of LiNi_0.5Mn_1.5O₄ (P4₃32 and Fd-3m) is ferrimagnetic state in which the Ni and Mn sublattices are ferromagnetically ordered along the 110 direction whereas they are antiferromagnetic with respect to each other. We demonstrate that it is the presence of O-vacancy in LiNi_0.5Mn_1.5O_4-δ with the Fd-3m space group that results in its superior electronic conductivity compared with LiNi_0.5Mn_1.5O₄ with the P4₃32 space group.