Our research is focused on the structural characterisation of ordered and disordered functional materials in the solid state, using powder diffraction, solid-state NMR spectroscopy and first-principles DFT calculations. In particular, we are interested in perovskite-based systems and their use in a wide range of devices and applications, including electronics and energy storage devices.

The alkaline niobates, NaNbO₃, KNbO₃ and the solid-solution K_xNa_1−xNbO₃ (KNN) are of considerable interest owing to reports of exceptional piezoelectric responses, believed to be comparable to those of the most widely used piezoelectric ceramic, Pb(Zr_xTi_1−x)O₃ (PZT). The work presented here focuses on the room temperature phases of NaNbO₃, which remain a subject of considerable discussion.^[1] Several phases have been suggested and observed experimentally, including the antiferroelectric Pbcm and polar P2₁ma polymorphs of NaNbO₃.^[2] The relative quantities of these two phases are known to vary considerably depending on the precise synthesis conditions used, e.g., conventional solid-state techniques versus molten salt and sol-gel approaches. Here, high-resolution powder diffraction and solid-state NMR data will be presented comparing the different synthetic techniques used.^[2]

All-solid-state lithium-ion (Li-ion) batteries are attracting considerable attention as possible alternatives to conventional liquid electrolyte-based devices as they present a viable opportunity for increased energy density and safety. In recent years, a number of candidate materials have been explored as possible solid electrolytes, including garnets, Li-stuffed garnets, Li-rich anti-perovskites (LiRAPs) and thio-LISICONs. In particular, LiRAPs, including Li_3−xOH_xCl, have generated considerable interest, based on their reported ionic conductivities (~10⁻³ S cm⁻¹).^[3,4] However, until recently, their lithium and proton transport capabilities as a function of composition were not fully understood. Hence, current research efforts have focused on the synthesis and structural characterisation of Li_3−xOH_xCl using a combination of ab initio molecular dynamics and variable-temperature ¹H, ²H and ⁷Li solid-state NMR spectroscopy. We will demonstrate that Li-ion transport is highly correlated with the proton and Li-ion vacancy concentrations. In particular, we will show that the Li ions are free to move throughout the structure, whilst the protons are restricted to solely rotation of the OH⁻ groups. Based on these findings, and the strong correlation between long-range Li-ion transport and OH⁻ rotation, we have proposed a new Li-ion hopping mechanism, which suggests that the Li-rich anti-perovskite system is an excellent candidate electrolyte for all-solid-state batteries.^[5] However, to fully understand the mechanism for conduction, multiple, complementary characterisation techniques are needed.