Structural, morphological, and electric study of doped- Na2Zn2TeO6 family in a wide range of temperatures

Abstract

Nowadays Sodium solid conductors are intensely studied to develop electrochemical energy storage devices to boost the development of sodium ion batteries. The Na₂Zn₂TeO₆ (NZTO) has been stablished as a 2D Na-ion conductor with excellent performance at low temperature. In this work four doped-NZTO have been synthesized by solid state reaction. The metal cations incorporated were: Ba²⁺, Nb⁵⁺, Mo⁶⁺, W⁶⁺. Their structures were characterized by XRD as a function of the temperature, and the Rietveld and Le Bail refinement were applied. Also, the thermal stability was studied by DSC technique between −40 °C to 400 °C. SEM, EDS and density measurement complement the information on structural features. The electrical conductivity, studied by impedance spectroscopy and DC polarization, confirmed that it is possible to minimize the inherent electronic conductivity and that the material’s best performance, as a pure sodium conductor, was achieved at low temperature Moreover, this technique confirmed that the presence of a reversible order/disorder transition of sodium ions /vacancies in the structure has an important effect on the total conductivity. Additionally, it was analyzed how to minimize the sodium loss during the sintering process to diminish the secondary phase formation.