Transition Metal Dopant Cation Distributions in MgO and CaO: New Inferences from Paramagnetically Shifted Resonances in 17O, 25Mg, and 43Ca NMR Spectra

We report on paramagnetic shifts identified in 17 O, 25 Mg, and 43 Ca NMR spectra of CaO and MgO doped with 0.3–2.2 mol % NiO or CoO. Systematically shifted features were identified for both paramagnetic dopants (Ni 2+ or Co 2+ ) and both bulk materials (CaO and MgO), and in some cases spectral features could be assigned to paramagnetic cations at specific sites within five bonds of the observed nucleus. We compare the empirical peak areas to theoretically derived peak areas expected under conditions of random mixing and observe that Ni 2+ - and Co 2+ -doped MgO systems agree well with random mixing but doped CaO systems do not. In spite of the very low natural isotopic abundances of 17 O and 43 Ca, moderate natural abundance of 25 Mg, and relatively low Larmor frequencies of all three nuclides, the cubic crystal structures and the resulting narrow NMR peaks allowed a first look at the potential of investigating dopant cation distributions in group 2 oxides though NMR.