Chapter 9: NMR at High Temperature Check Access

In this chapter, the motivations for developing in situ, high-temperature NMR methods are discussed, challenges for such measurements are presented, and applications to solid, glassy and molten inorganic materials are given. High-temperature NMR is uniquely suited for measuring rates of cation and anionic site exchange, of re-orientation and bond-breaking in structural groups, and of dynamical changes in symmetry, for processes occurring at time scales from seconds to nanoseconds. These kinds of dynamics are often at the heart of macroscopic properties including diffusivity, conductivity and viscosity, and of crystallographic and glass-to-liquid transitions. In high-temperature liquids such as molten oxides and fluorides, NMR at temperatures as high as 2500 °C can provide information on averaged local structure and how it changes with temperature and composition. High-resolution MAS NMR spectra can be collected to temperatures as high as 700–900 °C, albeit at relatively modest spinning rates, and can reveal dynamics of site exchange for resonances separated by only a few ppm. High-temperature single crystal spectra may provide enhanced resolution to detect symmetry changes and dynamics; both single crystal and powder spectra for nuclides with spin >½ can again detect motional processes that affect the magnitude and symmetry of electric field gradients.