Micromechanical Assessment of Al/Y-substituted NASICON Solid Electrolytes

Al/Y-substituted NASICON solid electrolytes are promising for novel solid state batteries. The solid solutions Na1+2xAlxYxZr2-2x(PO4)3 (NAYZPx) and Na3+2xAlxYxZr2-2x(SiO4)2(PO4) (NAYZSiPx) that crystallize in this structure are characterized by depth-sensitive indentation technique to determine their micro-mechanical properties. NAYZPx is rhombohedral, whereas NAYZSiPx changes from monoclinic to rhombohedral phase depending on substitutional level and temperature. For rhombohedral NAYZPx elastic moduli are in the range ~72–82 GPa and hardness values are in the range ~4.8–5.8 GPa, whereas for NAYZSiPx the elastic moduli are with the range ~72–88 GPa and hardness ~5.6–7.6 GPa, respectively. The fracture toughness values for both systems, as determined by Vickers indentation, are rather independent of the applied load being with the range 1.30–1.58 MPa m0.5. Cracks typically show a mixed intergranular/transgranular crack mode