The use of hot-pressing to reduce grain boundary resistance in Nasicon of nominal composition Na3Zr2Si2PO12

Abstract

Nasicon powders of nominal composition Na3Zr2Si2PO12 were hot-pressed at temperatures of 1150, 1200 and 1250 °C. At room temperature a total conductivity of 4.2 × 10−3 S/cm was exhibited, approaching bulk conductivity values (5–6 × 10−3 S/cm). The results of impedance spectroscopy combined with microstructural examination and analytical electron microscopy suggested that the high conductivity is a result of the applied stress during hot-pressing. It is believed that the applied stress at high temperatures causes expulsion of molten glass, thereby reducing the thickness of the high resistance glassy phase along Nasicon grain boundaries. This leads to reduced grain boundary resistance and hence, a higher total conductivity than that observed for sintered samples, where no applied stress is present.