Na-ion diffusion in the layered oxide Na2Zn2TeO6

The future of solid-state battery technology relies on solid electrolytes. The main key factors are its thermodynamical stability, conductivity, cost, and abundance. So far lithium-ion batteries are the main workhorse; however, their limited availability and high cost are the bottlenecks for many high energies and high power applications such as electric vehicles. Sodium-ion batteries are considered to be the best alternative energy storage technologies.
The compound Na2Zn2TeO6 (NZTO) crystallises in the pure P2-type phase (P6322) at a synthesis temperature of 1173 K. The pure P2-phase layered structure of NZTO compounds shows fast Na+ conductivity (σ = ⁓ 4×10-4 S/cm) and low activation energy (⁓ 0.29 eV) at room temperature. We propose to perform the quasielastic neutron scattering (QENS) in the P2-phase of NZTO to explore Na ion's single ion and collective dynamics. We have measured the phonon density of states at MARI for measurements and observed large phonon softening of low energy modes in NZTO above 500 K. At elevated temperatures, the large population of such low energy anharmonic modes may onset the Na diffusion. We anticipate the evolution of QENS signal at above 500 K, which validates that the role of strongly anharmonic modes on fast Na diffusion. Hence the proposed QENS measurements would be useful to understand the fast Na diffusion in NZTO and correlation with low-E soft anharmonic vibrational modes.