Lindsay S. Cahill

High-resolution solid-state 7Li NMR was used to characterize the structure and dynamics of lithium ion transport in monoclinic Li3V2(PO4)3. Under fast magic-angle spinning (MAS) conditions (25 kHz), three resonances are clearly resolved and assigned to the three unique crystallographic sites. This assignment is based on the Fermi-contact delocalization interaction between the unpaired d-electrons at the vanadium centers and the lithium ions. One-dimensional variable-temperature NMR and two-dimensional exchange spectroscopy (EXSY) are used to probe Li mobility between the three sites. Very fast exchange, on the microsecond time scale, was observed for the Li hopping processes. Activation energies are determined and correlated to structural properties including interatomic Li distances and Li−O bottleneck sizes.

Plastics are ubiquitous and, when released into the environment, break down into smaller particles termed microplastics (MPs) and nanoplastics (NPs). These MPs and NPs can be ingested by organisms and potentially accumulate in tissues and organs. Recently, MPs were found in the placentas of healthy women, raising the concern that exposure to plastics may have an impact on pregnancy and fetal development. In this study, we investigated the effect of maternal exposure to plastics on fetal and placental growth using experimental mice. The dams exposed to plastics received either 5 μm or 50 nm polystyrene plastics in filtered drinking water at one of three concentrations (102, 104, or 106 ng/L). In late gestation, MP- and NP-exposed fetuses were significantly growth restricted, with a 12% decrease in fetal weight at the highest exposure concentration. This study represents a crucial first step toward evaluating the risks to human pregnancies posed by exposure to plastics.

Studies of Li[Ni1/3Mn1/3Co1/3]O2 prepared under six different conditions are compared using high-resolution solid-state 6Li NMR. Differing degrees of cation disorder are established via integration of the NMR resonances, and this quantification of cation disorder is compared with Rietveld refinements of powder X-ray and neutron diffraction studies. Chemical shift trends to high frequency with decreasing degrees of disorder are established among this family of samples and explained according to the orbital overlap experienced by Li nuclei in the two environments: within the lithium layers and exchanged with nickel into the transition metal layers. Finally, an interesting case of local transition metal charge ordering is observed. Three unique environments are described, which can be accounted for based on electroneutrality arguments, and the known clustering of Ni2+ and Mn4+. This effect has not been detected in these materials by other methods including neutron and X-ray diffraction. Thus, the local ordering, which is observed in the dominant NMR resonance of Li in its own layers is thought to be pervasive (affecting the majority of the NMR nuclei), but very local, so as to be seen only by techniques such as NMR which probe immediate neighborhoods.