A Comparative Investigation on the JT Effect in Triangular Compounds of NaMnO₂, NaNiO₂ and NaTiO₂

We present a study on the Jahn–Teller (JT) distortions of the TiO₆, NiO₆ and MnO₆ complexes in NaTiO₂, NaNiO₂ and NaMnO₂ triangular compounds with a C_2/m structure. The JT vibronic normal modes are found to be Q₃, Q^'₄ and Q₆ by the group symmetry on the C_2/m structure. The magnitude of the normal coordinates (Q₃, Q^'₄, Q₆) and the structural parameters of distorted octahedra MO₆ (M=Ti, Ni, Mn) are obtained and in good agreement with experimental data. The energy level splitting of 3d orbitals and the highest occupied molecular orbital (HOMO) character in the MO₆ complex are also calculated in accordance with the JT distortions. These results provide a first insight into the groundstate and magnetic properties of distorted triangular compounds AMO₂.