Na-ion diffusion in the layered oxide Na 2 Zn 2 TeO 6

The compound Na2Zn2TeO6 (NZTO) crystallizes in the pure P2-type phase (P6322) at a synthesis temperature of 1173 K and above. The pure P2-phase has a layered structure and shows fast Na+ conductivity (σ = ⁓4×10-4 S/cm) and low activation energy (⁓0.29 eV) at room temperature. The high Na-ion conductivity for the P2-phase of NZTO at room-temperature attracts much attention. Our earlier QENS measurements on OSIRIS as well as phonon measurements on MARI along with ab-initio calculations were used to understand the Na/Li-ion diffusion in Na2Ti3O7, Na2Si2O5 and Li2Si2O5. Our recent AIMD simulations in the P2-type phase show that Na diffuses in a 2d-layer formed between the layers of ZnO6/TeO6 octahedral units, and the estimated diffusion constants is ~4x10-6 cm2/sec at 700 K. We propose to perform the QENS and INS measurements in the P2-phase of NZTO to investigate the effect of doping on the phonon spectrum and Na diffusion and their possible interplay. We expect significant changes in the phonon spectrum with temperature associated with Na vibrations. These measurements would help to understand the large diffusion behavior in layered NZTO compound and their relation with phonons. We expect the hopping of Na-ion would manifest as a strong quasielastic signal.