Local coordination of Fe(3+) in layered LiCo(1-y)Al(y)O(2) oxides determined by high-frequency electron paramagnetic resonance spectroscopy.

The local coordination of Fe(3+) spin probes in trigonal LiAl(y)Co(1-y)O(2) was studied using high-frequency electron paramagnetic resonance spectroscopy. This technique allows the determination of Fe(3+) ions in respect to axial and rhombic zero-field splitting parameters (ZFS). After the progressive replacement of Co by Al, the axial D parameter of Fe(3+) increases from +0.0548 to +0.2802 cm(-1). On the same order, the rhombic E parameter decreases. Structural information about the Fe(3+) site in layered LiAl(y)Co(1-y)O(2) oxides was based on modeling of the magnitude of the ZFS parameters by means of the Newman superposition model. It was found that the first metal coordination sphere including Co(3+) and Al(3+) ions gave rise to differentiation of the Fe(3+) dopants in respect to local trigonal and rhombic distortion. The maximum trigonal distortion for the FeO(6) octahedron was achieved when Fe(3+) spin probes were surrounded by Al only, while the Co environment yields a rhombic distortion of the FeO(6) octahedron.