Ionic conductivities of Na–Ge–P glass ceramics as solid electrolyte

• Glass formation range and stable phase formation range are studied in this paper.
• The phase structure of NaGe2(PO4)3 is observed by XRD and microscopic structure is observed by SEM.
• NYGGP shows superior conductivity and low activation energy at 300 °C.

In order to meet the need for sodium secondary batteries, a new system of Na1+xYyGax−yGe2−x(PO4)3 glass ceramics is prepared by heating at 1400 °C in glass formation range and transformed from glass to glass ceramics by reheat treatment. By investigating the phase structure by XRD spectra and microstructure by SEM, the NaGe2(PO4)3 with grain size around 1 μm is the main crystal phase of the obtained glass ceramic materials. Also, the conductivities of the glass ceramics with different doping density of Y3+ are tested by electrochemical impedance spectroscopy technique. As a result, the conductivities are increased with the increase of doping density of Y3+ and the ionic conductivities of Na1+xYyGax−yGe2−x(PO4)3 (NYGGP) are 1.40 × 10−3 S cm−1 at 300 °C and 1.15 × 10−5 S cm−1 at room temperature, the activation energy is 20.5 kJ/mol at 300 °C.