From the present understanding of

From the present understanding of cold sintering, densification is obtained through a dissolution and re-precipitation process [16]. Therefore, we assumed that LSZG could readily dissolve in water under the temperatures used in this study. X-ray diffraction patterns of CSP at 140 °C and 200 °C, and conventionally sintered at 1150 °C samples were all measured between 15° and 45°, shown in Fig. 4. Since there was possibility that the dense sample had different crystal structure on the surface and inside, the samples were ground to a powder by mortar and pestle before XRD measurement. The diffraction peaks of conventional sintered sample are the same as prepared LSZG powder, and there are no detectable second phases. In contrast, we detected Li2GeO3 (#04–008-3006 [17]) as a secondary phase whose diffraction peaks increased in intensity with increasing sintering temperature. Therefore, we assumed that because LSZG incongruently dissolves in water, second phase is precipitated out during CSP.