Electrical conductivities were meas

Electrical conductivities were measured at 25℃ and intervals of 50℃ during the heating process from 50℃ to 400℃,and also each temperature step was stabilized with 10 min holding times before starting the impedance measurement. Figure 9 shows typical Nyquist plots of measured impedance spectroscopy data, and Table 2 shows fitted value of total resistance. A measured lithium ionic conductivity, shown in Fig. 10, indicates conventionally sintered and annealed cold sintering samples have similar properties. Recent work of pure Li14Zn(GeO4)4 by Hong et al. is also plotted in Fig. 10 as a reference value [4]. The result shows conventionally sintered sample and annealed cold sintering samples have similar conduction property in a temperature range between 25℃ and 400℃, and conductivity is, respectively, 2.3 × 10−2 Scm−1 and 3.0 × 10−2 Scm−1 at 400 °C. We assumed that the annealed CSP sample has smaller grain size than the conventional sintered material, see Fig. 7, but clear grainboundary was also formed; therefore, the conductivity does not change between each sample, suggesting there are no issues with rate limiting conduction at the grain boundaries. Theactivation energy of lithium conductivity was also estimated in a temperature range of between 25 °C and 400 °C [21, 22].