Local Coordination of Fe3+ in Layered LiCo1-yAlyO2 Oxides Determined by High-Frequency Electron Paramagnetic Resonance Spectroscopy.

The local coordination of Fe[sup3+] spin probes in trigonal LiAl[suby]Co[sub1-y]O[sub2] was studied using high-frequency electron paramagnetic resonance spectroscopy. This technique allows the determination of Fe[sup3+] ions in respect to axial and rhorhbic zero-field splitting parameters (ZFS). After the progressive replacement of Co by Al, the axial D parameter of Fe[sup3+] increases from +0.0548 to +0.2802 cm[sup-1]. On the same order, the rhombic E parameter decreases. Structural infoiLmation about the Fe[sup3+] site in layered LiAl[suby]Co[sub1-y]O[sub2] 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[sup3+] and AI[sup3+] ions gave rise to differentiation of the Fe[sup3+] dopants in respect to local trigonal and rhombic distortion. The maximum trigonal distortion for the FeO[sub6] octahedron was achieved when Fe[sup3+] spin probes were surrpunded by Al only, while the Co environment yields a rhombic distortion of the FeO[sub6] octahedron. [ABSTRACT FROM AUTHOR]