All the synthesis work above was performed, and all synthesized products were transferred to, an argon-filled glovebox (200 B, MBraun, Germany; H2O < 0.4 ppm, O2 < 0.1 ppm). Ball milling jars are sealed and opened under the same argon atmosphere. All the unit cell parameters and detailed information about constraints can be found in Tables . Electrochemical Impedance Spectroscopy. Electrochemical impedance spectroscopy (EIS) was used to study the ionic conductivities and activation energy of the samples. Sample powder was filled in a 12 mm diameter polyether ether ketone (PEEK) die with an architecture {hard metal |SSE| hard metal} symmetric cell and cold-pressed pellets were prepared under an applied pressure of 430 MPa for 1 h in a CompreDrive instrument from rhd instruments GmbH. The hard metal is tungsten carbide which functions as Na + blocking layer. The impedance measurements were carried out using an SP-200 potentiostat (Biologic) applying an AC amplitude of 100 µA (GEIS) and frequencies in the range of 200 MHz to 100 mHz. Spectra were collected under different pressures (2 Mpa to 400 Mpa) and at different temperatures of 5 to 55 ℃. To obtain reliable fitting results, the ultrahigh frequency range was discarded due to the inductor influence from instrumental interconnection. Activation energies were derived from a linearized Arrhenius plot: ln(σT) ∝ 1/T.