Divalent-dopant criterion for the suppression of Jahn-Teller distortion in Mn oxides:First-principles calculations and x-ray absorption spectroscopy measurements for Co in LiMnO2

Co doping on the Mn sublattice of layered LiMnO2 suppresses the Jahn-Teller-driven monoclinic distortion in favor of a layered rhombohedral structure. First-principles calculations (within the local-spin-density approximation-generalized-gradient approximation frame-work) using the VASP code, as well as x-ray absorption measurements, elucidate the effect of the Co doping on the atomic structure and the charge states of Mn and Co. The analogy between Li manganate and La manganite suggests that dopants of either system that are divalent in both the distorted antiferromagnetic phase and the symmetric ferromagnetic phase are most effective in suppressing the cooperative Jahn-Teller distortion.