Theoretical investigation for the EPR g factors and the local structure for the two tetragonal Ni3+ centers in ACoO2 (A = H, Li)

• SH parameters and local structures are analyzed for ACoO2:Ni3+ (A = H, Li).
• Ligand orbital and spin-orbit coupling contributions are included.
• Ligand octahedra experience relative elongations 2.57% (and 1.6%) along C4 axis.

The electron paramagnetic resonance g factors and the local structure for the tetragonal Ni3+ centers in HCoO2 and LiCoO2 are theoretically studied from the perturbation formulas of the g factors for a 3d7 ion with low spin (S = 1/2) in tetragonally elongated octahedra. In these formulas, the related molecular orbital coefficients are quantitatively determined from the cluster approach in a uniform way. According to the calculations, the ligand octahedra around Ni3+ are suggested to suffer relative elongation 2.57% (and 1.6%) along the [0 0 1] (or C4) axis for the tetragonal Ni3+ centers in HCoO2 (and LiCoO2), due to the Jahn–Teller effect. The calculated g factors based on the above Jahn–Teller elongations are in good agreement with the observed values.