Supertransferred Hyperfine Fields at7Li: Variable Temperature7Li NMR Studies of LiMn2O4-Based Spinels

Abstract

The temperature dependence of the 7Li NMR shift was measured for LiMn2O4, LiMn2-yNiyO4 (y = 0.1, 0.25, 0.33), LiMn2-yCoyO4 (y = 0.25, 0.5, 1.0), Li[Mn2-yLiy]O4 (y = 0.1, 0.33), and λ-MnO2 spinel oxides. The 7Li NMR shift can be separated into temperature-independent and -dependent components. The temperature-dependent shift follows the Curie−Weiss behavior of the bulk magnetic susceptibility. The temperature-independent shift is attributed to contributions from van Vleck and diamagnetic susceptibilities. Pauli susceptibility may also contribute to the temperature-independent shift in the nickel- and cobalt-substituted spinels. Supertransferred hyperfine (STH) coupling constants were derived from the 7Li NMR shifts and bulk magnetic susceptibility data. The progressive increase in average nominal manganese oxidation state from +3.5 to +4 results in an increase in the supertransferred hyperfine field at the 7Li nucleus in the lithium-substituted samples. Replacement of manganese by either cobalt or nickel a...