Cold sintering for Li_1.5Al_0.5Ge_1.5(PO₄)₃ using LiNO₃-LiOH as a transient solvent

Abstract The cold sintering process (CSP) is an innovative technique to densify ceramic powders at ultralow temperatures by applying uniaxial pressure and using a transient solvent. However, obtaining dense Li1.5Al0.5Ge1.5(PO4)3 (LAGP) ceramics, which have high ionic conductivity, by CSP has been a challenging subject, because incongruent dissolution from the powder to a solvent can happen during CSP, and that deteriorates the grain boundary. In this study, LiNO3-LiOH salt is used as the transient solvent to suppress the incongruent dissolution. LAGP ceramics densified by the CSP at 220 °C and 400 MPa for 5 h have no damage at the grain boundary. As the result, the total ionic conductivity reaches 1.9 × 10−5 S cm−1, which is the highest value ever reported among LAGP ceramics prepared by CSP only using inorganic materials.