Local environment and lithium ion mobility in lithium niobate (LiNbO2): inferences from structure, physical properties, and NMR

The structure and properties of LiNbO[sub 2], including the mobility of lithium ions, have been determined by Rietveld refinement of the structural model from powder neutron diffraction data and by analysis of [sup 93]Nb and [sup 7]Li NMR spectra, magnetic susceptibility data, and the optical spectrum. The material prepared for this study was found to be slightly deficient in lithium (relative to niobium), Li[sub 0.96]NbO[sub 2] from chemical analysis and Li[sub 0.98]NbO[sub 2] from the analysis of neutron diffraction data, but fully stoichiometric in oxygen. Close agreement between the lithium content and the lithium site occupancy suggests that there are few antisite defects, if any. The structural model for LiNbO[sub 2] first proposed by Meyer and Hoppe was confirmed by the refinement of the structural model from the powder neutron diffraction data; the static quadrupolar and dipolar interactions obtained from the NMR spectra are also consistent with this model. While impure samples are paramagnetic and exhibit field-dependent magnetic behavior, the purest samples are diamagnetic, and there is no field dependence. An absorption onset at approximately 2 eV was observed, providing further evidence that LiNbO[sub 2] is indeed a diamagnetic semiconductor, as predicted by the band structure calculation of Burdett andmore » Hughbanks. 24 refs., 7 figs., 1 tab.« less