Remediation of activation energy anomalies, scaling distortions, and bandwidth limitations in superionic conductivity modeling of NZSP NaSICON synthesized by an augmented SSR method

Less constrained by bandwidth limitations and sampling scarcity, broadband profiling in a wide temperature range, starting at the cryogenic threshold at-150 degrees C and extending to 200 degrees C, can be used to derive parameters of minimal variance for the Jonscher power law for ionic conductivity; these are employed to model the supe-rionic regime over elevated temperatures and frequencies beyond the limits accessed by contemporary elec-trochemical impedance spectroscopy (EIS) equipment. We apply this technique to non-stoichiometric NaSICON based on the canonical NZSP formula with 5% excess sodium, synthesized by an augmented solid-state reaction (SSR) method. We thoroughly analyze broadband conductivity, dielectric permittivity, and electric modulus data over the extended temperature range. Activation energy anomalies and scaling distortions inherent to the Arrhenius approximation are investigated, and an alternative formulation based on linearized difference equa-tions is proposed to remedy these issues. With Cole-Cole analysis establishing non-Debye relaxation behavior, dissipation analysis is employed to identify relaxation bands, used for extracting initial condition parameters for the Jonscher power law. Finally, simulations of the AC dispersion region at high temperatures and frequencies suggest the dominance of polaron tunneling mechanisms instead of the classical ion hopping mechanism assumed for NaSICON, in line with the latest insights on superionic conduction.

Automated summary

By conducting broadband profiling in a wide temperature range, we can model the behavior of superionic materials at high temperatures and frequencies beyond the limitations of traditional impedance spectroscopy equipment. Applying this technique to NaSICON materials, we analyzed their conductivity, dielectric permittivity, and electric modulus over an extended temperature range. We proposed an alternative formulation based on linearized difference equations to address issues with the Arrhenius approximation commonly used in these analyses. Through Cole-Cole analysis and dissipation analysis, we identified relaxation bands and extracted initial condition parameters for the Jonscher power law. Simulations of the AC dispersion region at high temperatures and frequencies suggested that polaron tunneling mechanisms dominate in NaSICON, in line with recent insights on superionic conduction.