Characterization of Na2Zn2TeO6 ceramic solid electrolyte densified by hot pressing

Abstract In this work, we applied hot pressing (HP) for the densification of Na 2 Zn 2 TeO 6 (NZTO) at lower temperature than conventional furnace sintering (FS). Calcined NZTO powder was densified by HP at 700°C for 1 h under uniaxial pressure of 20 and 60 MPa using a graphite mold. By increasing the uniaxial pressure to 60 MPa for HP, high relative density above 90% was obtained. As‐prepared NZTO by HP showed total (bulk + grain‐boundary) ionic conductivity of 0.29 mS cm −1 at room temperature, which is lower than NZTO prepared by FS at 800°C (=0.4 mS cm −1 ) with lower relative density (<85%). It was found that the contribution of grain‐boundary resistance in as‐prepared NZTO by HP is larger than NZTO by FS. We confirmed that the grain‐boundary resistance was significantly reduced by post‐annealing. Consequently, total conductivity at room temperature was improved to 0.42 and 0.56 mS cm −1 by annealing at 700 and 800°C for 2 h, respectively. X‐ray photoelectron spectroscopy analysis indicated that the residual carbon‐contained secondary phases were reduced by post‐annealing. These secondary phases could be formed by the carbon contamination from a graphite mold used for HP, and their removal by post‐annealing results in the improvement of ionic conduction at grain‐boundary.