Impact of Precrystallized NaYSi<sub>4</sub>O<sub>12</sub> Powders in the Synthesis of Sodium Conducting Solid Electrolytes
Dörte Wagner, Jochen Schilm, Chang Woo Lee, Mihails Kusnezoff
Abstract
The glass crystallization route for Na‐ion conducting glass ceramics with conductive N5 modification of Na 5 YSi 4 O 12 has been explored. P 2 O 5 is used to modify the glass frit for optimization of the sintering and crystallization process. Mass spectroscopy reveals that the evaporation of CO 2 in the sintered microstructure is responsible for enhanced porosity. The glass is not fully transformed to the highly conductive phase (N5) by crystallization and thereby lower conductivities in sintered samples is observed. A pre‐crystallization step of the initial glass powder is evaluated as suitable to eliminate the gas evolution and subsequent sintering of material crystallized in desired N5 modification is successfully performed. With the powder of the pre‐crystallized material, homogenous sintered microstructures consisting of crystalline and glassy phases are obtained. Despite the higher temperature needed for sintering, low porosity and a mechanical strength up to 60 N mm −2 are achieved for samples from pre‐crystallized powder. The analysis of impedance spectra of sintered samples reveal high impact of grain boundaries on total ionic conductivity. Samples made from pre‐crystallized powder show higher overall ionic conductivity of 8.3 × 10 −6 S cm −1 at room temperature which is lower than the conductivity of crystallized N5 phase grains (1.4 × 10 −4 S cm −1 ).