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The temperature dependence of the 7 Li NMR shift was measured for LiMn 2 O 4 , LiMn 2-y Ni y O 4 (y ) 0.1, 0.25, 0.33), LiMn 2-y Co y O 4 (y ) 0.25, 0.5, 1.0), Li[Mn 2-y Li y ]O 4 (y ) 0.1, 0.33), and λ-MnO 2 spinel oxides. The 7 Li NMR shift can be separated into temperature-independent and -dependent components. The temperaturedependent shift follows the Curie-Weiss behavior of the bulk magnetic susceptibility. The temperatureindependent 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 7 Li 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 7 Li nucleus in the lithiumsubstituted samples. Replacement of manganese by either cobalt or nickel also results in a larger STH field at the 7 Li nuclei. The increase in STH field for the lithium-, nickel-, and cobalt-substituted spinel oxides may arise from a greater covalence in these materials relative to the parent LiMn 2 O 4 spinel oxide.

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The relative arrangement of sodium and lithium ions in mixed-alkali silicate glases of composition [(Li 2 O) 1-y (Na 2 O) y ] x [SiO 2 ] 1-x (y ) 0.25, 0.50, and 0.75; x ) 0.40 and 0.50) is studied by 23 Na-{ 7 Li} spin echo double-resonance (SEDOR) NMR spectroscopy, supplemented by additional 23 Na-{ 6 Li} experiments on isotopically labeled materials. The experimental results are compared with various cation distribution scenarios and found to be quantitatively most consistent with a model in which lithium and sodium ions occupy random positions on a cubic lattice mimicking a uniform (homogeneous) spatial cation distribution. The experimental data give no evidence for preferred interactions among unlike cations or cation-pairing models previously invoked to describe the structure of mixed-alkali glasses. To the contrary, if the overall cation distribution were to diverge from homogeneous, the data would be most consistent with preferred interactions among like cations.

Modern solid state nuclear magnetic resonance (NMR) techniques afford powerful experimental strategies for elucidating detailed structural information in noncrystalline materials. While previous research emphasis has been on the identification and quantification of local environments (short-range-order), primarily by using the technique of magic-angle spinning (MAS) NMR, correlations beyond the nearest neighbor coordination sphere (intermediate-range order) can be studied by more sophisticated methods. This contribution focuses on recent advances made for a variety of oxide glasses, using methods of dipolar spectroscopy: Connectivities among the structural building blocks present in sodium aluminoborate glasses have been exposed using 11B[27Al] and 27Al{11 B} rotational echo double resonance (REDOR) NMR. Similarly, 29Si{31P] and 29Si[7Li) REDOR data form the basis of a structural model integrating six-coordinated silicon into the network structure of alkali silicophosphate glasses. The spatial cation distributions in sodium silicate glasses are studied by 23Na spin echo decay spectroscopy, offering experimental evidence for inhomogeneous cation distributions at low alkaline contents. Finally, for mixed alkali sodium lithium silicate glasses, 23Na{7LiJ spin echo double resonance (SEDOR) and 29Si[23Na} and 29Si[7Li} REDOR spectroscopies provide important experimental criteria for testing hypothesized relative Na-Li cation ordering scenarios.