Studies on the local structures for the trigonal Ni³⁺ centers in cathode materials LiAl_yCo_1–yO₂ (y = 0, 0.1, 0.5, and 0.8)

Abstract

The local angular distortions Δθ are theoretically studied for the various Ni centers in LiAl Co O at different Al concentrations (y = 0, 0.1, 0.5, and 0.8) based on the perturbation calculations of electron paramagnetic resonance g factors for a trigonally distorted octahedral 3d cluster with low spin (S = 1/2). Due to the Jahn-Teller effect, the [NiO ] clusters are found to experience the local angular distortions (Δθ ≈ 5°-9°) along the C axis. The variation trend of Δθ with y is in accordance with that of anisotropy (Δg = g - g ). As the substitutions can weaken bond strengths between transition metal and oxygen and the structural stability plays an important role in cathode performances, detailed investigations on the structural properties of the cathode materials LiAl Co O can be practically helpful to understand the performances of these materials. The oxy-redox properties of LiAl Co O systems are comprehensible in the framework of Ni /Ni couples, and the trigonally compressed octahedral [NiO ] clusters are applicable to the clarification of the electrochemical properties of lithium nickel oxide batteries. It appears that LiAl Co O with the largest Al concentration may correspond to the smallest distortion among the mixing systems.

Studies on the EPR parameters and local angular distortion for the tetragonal Cu2+ center in CaWO4 crystal

“…Thus, the molecular orbital coefficients N γ and λ γ can be determined from Equations 5, 6, and 7. Based on the free ion values ζ d 0 (Cu 2+ ) ≈ 829 cm À1 , [38] ζ p 0 (O 2À ) ≈ 151 cm À1 , [39] and P 0 ≈ 388 and 416 Â 10 À4 cm À1 for 63 Cu 2+ and 65 Cu 2+ , respectively, [40] the SOC coefficients (ζ and ζ 0 ), the orbital reduction factors (k and k 0 ), and the dipolar hyperfine structure parameters (P and P 0 ) were obtained from Equation 5, which are also listed in Table 1.…”